PHYS 


HYGIENE 


CONN 

AMD 

BUDIMGTOH 


SILVER,  BURDETT  ^  COMI'^AOT 


MEMCAL    SCHOOL 


>ard  of 
student 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/advancedphysioloOOconnrich 


ADVANCED    PHYSIOLOGY 
AND  HYGIENE 


FOR   USE  IN  SECONDARY  SCHOOLS 


BY 


,  t-? 


r^ 


HERBERT  W.OCONN,  Ph.D., 

FORMERLY   PROFESSOR  OF  BIOLOGY  IN   WESLEYAN    UNIVERSITY 
AND 

ROBERT  A.  BUDINGTON,  A.M., 

PROFESSOR  OF  ZOOLOGY  IN  ©BERLIN  COLLEGE 


REVISED  EDITION 


SILVER,  BURDETT  AND  COMPANY 

BOSTON        NEW  YORK       CHICAGO       SAN  FRANCISCO 


THE   CONN    SERIES   OF  PHYSIOLOGIES 

By  H.  W.  Conn,  Ph.D. 
Formerly  Professor  of  Biology,  Wesleyan  University 

Physiology  and  Health,  Book  One 
For  Lower  Grammar  Grades 
224  pages Illustrated 

Physiology  and  Health,  Book  Two 
For  Upper  Grammar  Grades 
384  pages Illustrated 

Physiology  and  Health,  One  Book  Course 

448  pages Illustrated 

Advanced  Physiology  and  Hygiene 

By  II.  W.  CcNN  AND  R.  A.  Budington 

For  Secondary  Schools 

41  g  Pages Illustrated 

Advanced  Physiology  and  Hygiene.    Revised  Edition 
436  pages Illustrated 


•  •     •     «•  1 

•  •    •  • 

a  •      •     • 

•  • ••    •  •      • ' 


■       •  •    •       •    •  r  t 

•••  •         •    »       f 


Copyright,  1909, 1919 
By  silver,  burdett  and  COMPAT^Y 


PREFACE 

When  the  science  of  physiology  was  first  introduced  into 
schools  the  texts  offered  for  study  treated  largely  of  anat- 
omy. As  the  subject  developed  and  expanded  it  was 
recognized  that  the  study  of  anatomy  should  be  made  sub- 
ordinate to  that  of  function,  and  the  text-books  came  to  give 
to  function  a  place  predominant  over  structure.  Further  ex- 
perience emphasized  the  fact  that  the  primary  utility  of  the 
study  of  physiology  in  schools  consists  in  its  bearing  upon 
health,  and  matters  of  personal  hygiene  came  to  occupy  a 
more  and  more  prominent  place.  Still  more  recently  problems 
of  public  hygiene  and  general  health  have  forced  them- 
selves to  the  front,  and  have  been  demonstrated  to  be  an 
important  part  of  a  person's  education.  With  this  broad- 
ening scope  and  all  these  new  aspects  of  life  and  health  to 
be  considered,  many  phases  of  the  subject  of  physiology 
proper,  themselves  of  scientific  interest  and  importance, 
have  inevitably  been  given  less  and  less  attentioHf^  while  the 
more  practical  topics  have  been  accorded  fitting  precedence. 

Although  perhaps  no  two  teachers  would  agree  as  to  the 
relative  importance  of  any  specific  topic,  certain  it  is,  how- 
ever, that  without  some  knowledge  of  anatomy,  physiological 
facts  seem  isolated  and  without  foundation;  while  rules  bear- 
ing on  hygiene,  taken  alone,  are  learned  by  the  student  mere- 
ly as  barren  rules  without  any  persuasive  reason  for  them. 
In  this  book  the  emphasis  placed  upon  different  subjects  is 
that  which  has  seemed  to  the  writers  to  be  a  close  approxi- 
mation to  their  relative  importance  in  the  present  state 
of  the  sciences   of  physiology  and  hygiene. 

This  book   has  one  new  feature  which  the  authors  feel 


4  PREFACE 

confident  will  commend  it  to  physicians,  health  officers  and 
public  spirited  citizens  generally.  In  connection  with  the 
different  systems  of  organs,  the  nature  and  causes  of  com- 
mon diseases  are  discussed  in  simple  terms  with  such  sug- 
gestions about  the  prevention  of  disease  as  may  help  ,to 
make  the  high  school  student  more  intelligent  in  regard 
to  his  own  health  and  the  health  of  the  community. 

In  the  treatment  of  the  problems  of  the  physiological  effects 
of  alcohol  it  is  assumed  that  students  using  this  book  are  of 
an  age  to  appreciate  that  some  of  the  many  problems  con- 
nected with  the  use  of  this  drug  are  still  unsettled.  Hence, 
while  some  aspects  of  this  subject  have  been  introduced  with- 
out anticipating  any  final  conclusion,  the  attempt  is  made 
to  point  out  the  most  important  of  the  evil  effects  resulting 
from  the  use  of  this  drug. 

The  revised  edition  contains  numerous  additions  to  the 
text  embodying  the  results  of  the  most  recent  scientific  investi- 
gations. Especial  attention  has  been  given  the  newer  con- 
ceptions of  proteid  digestion,  carbon  dioxid  in  respiration, 
vitamines,  the  role  of  certain  hormones,  and  the  etiology  of 
numerous  diseases.  Since  the  last  few  years  have  offered 
more  convincing  proof  than  ever  before  of  the  vital  relation 
between  hygiene  and  health,  sanitation  and  safety,  especial 
care  has  been  taken  to  rewrite  and  to  expand  the  chapter  on 
public  control  of  health.  The  number  of  laboratory  exercises 
and  demonstrations  has  been  materially  increased.  These 
have  been  assembled  in  a  separate  section  and  placed  in  the 
back  of  the  book  with  page  reference  to  the  portion  of  text 
to  which  each  applies. 

Robert  A.  Budington. 


CONTENTS 

CHAPTER  PAGE 

I.     The  Living  Material  of  the  Body       .  .       9 

Organs  and  Tissues.  Microscopic  Anatomy.  Uni- 
cellular and  Multicellular  Animals. 

II.     Chemical  Composition  of  the  Body      .  .     25 

Elements.  The  Chief  Chemical  Compounds  in  the 
Body,    Metabolism. 

III.  Foods  and  Food  Habits  .  .  .37 

Food  Habits.  The  Value  of  Different  Foods.  Diet. 
The  Amount  of  Food  Needed.  Vegetarianism.  In- 
cidental Articles  of  Food.    Cooking. 

IV.  Fermentation  and  Germ  Diseases         .  .     62 

Types  of  Fermentation.  Yeasts.  Bacteria.  Im- 
munity.    Sterilization  and  Disinfection. 

V.     Digestion  of  Food — The  Mouth  and  Throat     74 
The  Mouth.    Digestion  in  the  Mouth.    The  Throat. 
Diseases  of  the  Mouth  and  Throat. 

VI.     Digestion    of    Food — The    Oesophagus    and 

Stomach       .......     88 

The  Oesophagus.  Body  Cavity  and  Sub-Divisions. 
The  Stomach.  Composition  and  Action  of  the  Gas- 
tric Juice. 

VII.     Digestion  of  Food — The  Intestine      .  .     98 

The  Small  Intestine  and  Organs  Connected  with  It. 
The  Large  Intestine.  Digestion  of  Different  Foods. 
Alcohol  and  Indigestion.  Diseases  of  the  Intestinal 
Tract. 

VIII.     The  Absorption  of  Foods  .  .  .111 

Structures  Concerned  in  Absorption.  Osmosis. 
Changes  in  Food  after  Absorption.  The  Path 
taken  by  the  Absorbed  Carbohydrates  and  Pro- 
teids.  Path  taken  by  the  Fats.  Summary  of 
Digestion  and  Absorption. 


PHYSIOLOGY  AND  HEALTH 

CHAPTER  I 

THE  LIVING  MATERIAL  OF  THE  BODY 

''Know  thyself"  was  a  motto  of  the  ancient  Greeks.  Wise 
as  such  advice  was  in  their  day,  it  is  far  more  necessary  in 
these  modern  times  of  complex  civilization.  The  Greeks 
knew  less  than  we  of  the  activities  of  the  body  organs,  but 
they  needed  such  knowledge  less  because  their  mode  of  living 
was  simpler.  Their  lives  were  passed  largely  out  of  doors, 
never  in  close  houses;  their  food  was  plain,  but  nourishing 
and  abundant;  their  bodies  were  vigorous  and  active 
because  they  exercised  all  their  muscles. 

But  to-day  people  are  so  crowded  into  cities  that  there 
is  little  time  or  opportunity  for  physical  exercise  and  there  is 
every  facility  for  the  distribution  of  contagious  diseases. 
We  shut  ourselves  up  in  close  houses,  thus  depriving  ourselves 
of  needed  air;  we  use  trolleys,  carriages,  automobiles,  tel- 
ephones and  mails  to  save  the  time  and  trouble  of  walking, 
we  eat  an  endless  variety  of  good  and  bad  foods,  variously 
prepared  and  often  adulterated;  we  live  in  the  midst  of 
more  or  less  constant  and  intense  activity.  Brain  work 
takes  the  place  of  muscle  work  with  part  of  the  race  while 
another  part  uses  the  brain  very  little. 

Amid  all  these  complexities  the  problem  of  retaining  health 
and  vigor  is  increasingly  difficult.  In  our  crowded  cities 
people   are  living    under   unnatural    conditions,  and  serious 


10  ADVANCED  PHYSIOLOGY 

questions  are  constantly  arising  as  to  the  proper  means  for 
preserving  health.  Even  country  life  is  ceasing  to  be  the 
simple,  natural  life  that  it  was  once,  and  the  smaller  com- 
munities are  facing  many  of  the  problems  of  the  large 
cities.  With  each  succeeding  year  we  realize  more  fully  the 
need  of  understanding  the  laws  of  life  in  order  to  maintain 
both  individual  and  public  health.  All  this  makes  a  con- 
stantly increasing  demand  for  the  study  of  those  subjects 
which  teach  us  how  to  keep  our  bodies  and  minds  in  a 
state  of  highest  efficiency;  and  the  study  of  physiology  and 
hygiene  has  come  to  be  recognized  as  one  of  the  necessities 
of  education. 

Normal  and  Experimental  Physiology. — Physiology  is  the 
science  of  the  activities  of  living  things.  It  may  refer  to  the 
activities  of  animals  or  plants,  of  the  whole  animal  or  its 
parts,  of  the  whole  plant  or  its  parts,  or  even  of  whole 
groups  of  animals  or  plants.  If  observations  are  made 
upon  animals  under  healthy,  normal  conditions,  while  they 
are  acting  under  their  own  ordinary  impulses,  the  study 
is  called  normal  physiology.  Sometimes,  however,  an  animal 
or  a  plant  or  parts  of  either  may  purposely  be  put  under 
unnatural  conditions  and  the  result  noted.  We  may  change 
the  food  supply,  the  temperature  or  moisture  of  the  sub- 
stance in  which  it  lives,  we  may  try  the  effects  upon  it  of 
drugs  and  poisons,  or  we  may  artificially  stimulate  it  to 
action.  In  these  cases  the  study  is  termed  experimental 
physiology. 

The  term  physiology,  as  commonly  understood,  refers 
to  the  study  of  the  activities  or  functions  of  the  different 
parts  of  the  human  body  under  normal  conditions.  Although 
thus  primarily  a  study  of  activities,  some  attention  must 
also  be  paid  to  structure;  for  if  one  is  to  understand 
thoroughly  the  working  of  any  machine,  he  must  know  the 
form  and  position  of  its  parts.  The  study  of  the  structure 
of  the  body  is   called  anatomy.     Anatomy   and   physiology 


THE  LIVING  MATERIAL  OF  THE  BODY 


11 


are  thus  distinct  subjects,  yet  so  closely  related  that  they 
will  be  considered  separately. 

ORGANS   AND   TISSUES 

There  are  several  familiar  fundamental  facts  concerning 
living  things;  everyone  knows  that  the  commoner  animals 
feed,  breathe,  feel,  give  off  waste  material,  have  blood 
circulating  through  their  bodies  and  show  many  other  points 
of  similarity.  It  may,  however,  surprise  some  people  to  learn 
that  these  same  functions  are  carried  on  in 
plants,  for  they,  too,  must  feed,  breathe,  give  off 
waste  and  have  some  kind  of  circulatory  system, 
although,  to  be  sure,  these  life  processes  occur 
differently  in  animals  and  plants.  An  organism 
is  anything  which  carries  out  the  functions  of 
life. 

Certain  very  important  differences  exist  be- 
tween the  lower  (i.e.  microscopic)  organisms  and 
the  higher  ones.  In  many  of  the  lower  types 
of  animal  and  plant  Ufe  all  parts  of  the  body 
may  perform  the  same  office,  e.  g.  of  loco- 
motion, sensation  or  feeding;  but  it  is  apparent 
to  anyone  that  different  parts  of  the  human 
body  —  such  as  heart,  stomach,  brain  or  eye,  per- 
form each  its  own  work  or  function ;  and  each  is 
therefore  called  an  organ.  An  organ  may  be 
defined  as  a  part  of  the  body  which  has  one  special 
kind  of  work  to  do.  This  work  as  a  rule  contri- 
butes to  the  sustaining  of  every  other  part  of  the 
organism.  The  whole  body,  then,  may  be  pictured  as  com- 
posed of  many  separate  and  distinct  organs,  each  cooperat- 
ing with  the  other  and  thus  constituting  one  organism. 
Even  the  microscopic  animals,  hke  those  in  Figure  1,  have 
some  very  simple  organs,  as  for  instance,  the  nucleus  shown 
at  N, 


FiQ.  1.— Hy- 

ALODISCUS 
LIMAX 

A  microscopic 
animal  resem- 
bling amoeba, 
which  lives  in 
fresh  water. 
All  parts  of 
the  body  are 
nearly  alike 
and  perform 
the  same 
functions.  A^ 
is  the  nucleus. 


1^ 


ADVANCED  t>HYSIOLOGY 


Muscle 


This  study  of  the  parts  of  Hve  organisms  may  be  carried 
still  further;  and  just  as  the  stairway,  or  the  elevator,  or  the 
windows  of  a  house  are  not  made  entirely  of  wood,  or  of  iron, 
or  of  glass,  so  also  the  human  body  is  not  composed  through- 
out of  the  same  kind  of  material.  The  nose,  for  example,  is 
covered  with  skin;  is  lined  with  a  smooth,  moist  membrane; 
contains  a  supporting  framework,  partly  of 
soft  cartilage,  partly  of  bone;  blood  vessels 
are  present  in  it;  nerves  make  it  sensitive  to 
odors  and  to  touch;  hairs  are  provided  for 
straining  the  air  as  one  breathes;  muscles 
permit  shght  movements.  Such  parts  as 
these  composing  an  organ  are  commoidy 
called  tissues.  A  tissue  is  a  single  kind  of 
living  material  with  the  'power  of  doing  a 
single  kind  of  work.  Generally,  several  dif- 
ferent kinds  of  tissue  occur  in  the  structure 
of  a  single  organ.  The  hand,  for  example, 
contains  bone  tissue,  muscle  tissue,  nerve 
tissue  and  blood  tissue,  besides  several 
other  kinds. 

Kinds  of  Tissues. — The  following  are  the 
most  important  tissues  of  the  human  body. 
Epithelium,  or  covering  tissue,  is  a  thin 
layer  covering  the   outer   and  inner   sur- 
faces of  the  body  and  of  the   different   organs ;    e.  g.  the 
outer  layers  of  the  skin  and  the  lining  of  the  mouth  and 
throat. 

Supporting  tissues  include  bone,  cartilage  and  connective 
tissues.  Bone  forms  the  skeleton.  Cartilage  is  found  in  many 
different  regions  of  the  body.  It  is  placed  between  each  two 
pieces  of  the  'back-bone';  it  composes  the  principal  part  of  the 
voice-box;  it  makes  the  ears  and  the  nose  somewhat  rigid;  it 
covers  the  ends  of  bones  where  they  come  together  at  moving 


Tendon 


Fig.    2. — The    leg 

Showing  the  bones, 
mviscles  and  tendons 
concerned  in  hfting 
the  body  upon  the 
toes. 


THE    LIVING    MATERIAL    OF   THE    BODY 


13 


joints.  Sometimes  it  connects  the  bones,  e.  g.  as  it  joins  the 
front  ends  of  the  ribs  to  the  breast  bones.  Connective  tissue 
occurs  throughout  the  whole  body,  binding  together  the  dif- 
ferent parts.  A  simple  kind  of  connective  tissue  is  seen  in 
beefsteak,  where  it  appears  in  fine  lines  or  as  thin,  glistening 
sheets  holding  together  the  small  cord-like  pieces  of  muscle 
tissue.  More  evident  kinds  of  connective  tissue  are  the  liga- 
ments and  tendons;  Fig.  2.  Ligaments  hold  bones  together 
at  joints,  as  at  the  knee  or  the  shoulder.  Tendons  connect 
muscles  to  bones,  and  may 
plainly  be  felt  at  the  wrist 
where  they  pass  from  the 
muscles  in  the  forearm  to 
the  bones  in  the  fingers; 
Fig.  137.  It  is  said  that 
if  all  the  other  materials 
of  the  body  were  dissolved 
away  and  the  connective 
tissue  left,  this  tissue  is  so 
abundant  that  the  form  of 
the  body  would  be  per- 
fectly retained. 

Muscle  tissue  forms  the 
flesh  and  moves  the  differ- 
ent parts  of  the  body. 

Gland    tissue    composes 
organs  and  surfaces  which 
generally    produce     some 
fluid  secretion,   hke  the  saliva    in  the  mouth,  the  tears  in 
the  eyes  or  the  bile  in   the  liver. 

Blood  forms  the  so-called  "circulating  tissue." 

Nerve  tissue  is  the  material  of  which  the  brain  and  other 
parts  of  the  nervous  system  are  composed. 

Fat  tissue,  while  not  active,  serves  to  store  material  for 
future  use. 


Fig.  3. — Epithelial  cells 

a,  flat,  scale-like  cells  from  the  mouth; 

b,  from  the  membranes  around  the 
intestine;  c,  from  the  intestine;  d,  cili- 
ated epithelial  cells  from  the  wind  pipe. 


14 


ADVANCED   PHYSIOLOGY 


A  study  of  the  organs  and  tissues  of  an  organism  as  seen 
with  unaided  eye  is  called  a  study  of  its  macroscopic  anatomy. 
If  a  microscope  is  used,  one  is  said  to 
be  studying  its   microscopic  anatomy. 

MICROSCOPIC   ANATOMY 

After  the  invention  of  the  micro- 
scope by  two  Dutchmen,  Hans  and 
ZachariasJanssen,  about  the  year  1600, 
curiosity  gradually  led  to  the  examina- 
tion of  all  kinds  of  animal  and  plant 
substances  under  high  magnification. 
Of  special  interest  to  us  here  is  a  fact 
established  in  1838-1839,  that  all  tis- 
sues in  plants  and  animals  are  made  up  of  definitely  formed 
parts  or  units,  somewhat  in  the  manner  in  which  the  walls  of 
brick  buildings   are  made   up  of   separate  bricks. 

Bloodvessel^^   ^^ 


Fig.  4.— C  a  r  t  i  l  a  gj  e 

CELLS 

Embedded  in  an  abundant 

intercellular  matrix. 


Fig.  5. — The  microscopic  structure  of  bone 
^,  cross  section;  B,  longitudinal  section;  C,  a  single  young  bone  celi. 

These  small  units  had  been  seen  two  hundred  years  earlier  and 
at  that  time  were  called  cells,  since  it  was  thought  that  they  were 
practically  empty  pockets.  But  to  Schleiden  and  Schwann, 
who  first  demonstrated  that  all  tissues  are  made  up  of  such 


THE   LIMNG   MATERIAL  OF   THE   BODY 


15 


Fig.    6, — Connective    tissue 

A  bit  of  tendon  highly  magnified. 
At  C  are  shown  some  of  the  cells 
which  produced  the  fibres. 


cells,  is  given  the  main  credit  of  firmly  establishing  what  has 
since  been  known  as  the  cell  theory  of  tissue  structure. 

According  to  some  students  of  the  subject,  these  cells  are 
connected,  each  with  its  neighboring  cells,  by  very  tiny,  hollow 
tubes  (''bridges'');  but  others  are  equally  certain  that  each  cell 

acts  by  itself,  save  as  fluids  may 
pass  out  from  each  cell  and  be 
carried  to  otha?  cells  of  the  body 
in  tire  blood  stream. 

Kinds  of  Cells. — The  shape  of 
these  cells  is  difTerent  in  differ- 
ent kinds  of  tissues,  just  as  bricks 
used  in  the  foundations  of  build- 
ings differ  from  those  employed 
for  fireplaces  or  ornamental  work. 
Epithelial  cells  are  thin  and  disc-like  or  cylindrical  in  shape 
(Fig.  3  a,  6;  c  and  d)  and  usually  have  very  little  space  be- 
tween them. 

Cartilage  cells  are  round  or  hemi- 
spherical and  are  usually  more  widely 
separated;  Fig.  4.  The  material  be- 
tween them,  intercellular  substance,  has 
been  formed  by  the  cells  themselves 
and  secreted  in  large  quantities,  sep- 
arating them  as  mortar  does  bricks. 

Bone  cells  are  close  together  in  very 
young  bone,  but  later  are  separated  by 
a  secretion  which  they  deposit  around 
themselves.      This   deposit   contains    a 
mineral  matter,  calcium  phosphate,  which 
causes  the  mass  to  harden.    As  the  bone 
develops,  this  hard  mineral  matter  be- 
tween the  cells  becomes  very  abundant,  and  finally,  in  the  fully 
formed  bone,  the  cells  proper  occupy  very  small  spaces;  Fig.  5. 
Connective  tissue  shows  almost  no  cells  for  it  consists  for 
.e  most  part  of  numerous  fine  fibres,   frequently  arranged 


Fig.  7. —  Connective 

TISSUE 
The  soft  tissue  that  lies 
between  the  skin  and  the 
muscles.  Fibres  are 
shown  running  irregu- 
larly, and  some  cells,  C. 


16 


ADVANCED  PHYSIOLOGY 


in  bundles,  as  in  tendons  (Fig.  6) ;  or  in  confused  masses  running 
in  all  directions,  as  in  the  soft  mass  of  connective  tissue 
beneath  the  skin;  Fig.  7.  But  in  each  a  few 
genuine  cells  can  be  seen,  and  a  study  of  the 
growth  of  connective  tissue  shows  that  the  fibres 
are  really  produced  by  the  cells. 

Muscle  tissue  consists  of  fibres,  sometimes 
tapering  at  the  ends;  Fig. 8.  When  the  muscle 
contracts,  these  fibres  diminish  in  length  and 
thicken  in  the  middle.  Such  a  fibre  is  some- 
times a  single  muscle  cell,  and  sometimes  several 
cells  fused  together,  but  in  any  case  it  is  cellular. 
Gland  cells  are  frequently  cylindrical,  some- 
times nearly  spherical;  Fig.  9.  The  material 
they  secrete  collects  in  them  and  is  later  ex- 
pelled, either  continuously,  as  in  some  glands, 
or  at  intervals,  as  in  others. 

Blood  consists  of  many  cells,  called  blood 
<;orpuscles,  floating  in  a  liquid;  Fig.  10.  This 
liquid  is  not  formed  like  the  mass  of 
material  separating  the  cells  in  cartilage 
and  in  bone,  since  it  is  not  produced  by 
the  blood  cells  themselves. 

Nerve  cells  differ  widely  in  shape;  some 
are  nearly  round,  some  are  very  long  and 
some  are  irregular  in  outline.  A  com- 
mon type  has  an  angular  body  with  a 
few  much-branched  prominences  extend- 
ing from  the  corners;  Fig.  11. 

Fat  cells  are  like  some  of  the  other  cells 
of  the  body,  but  pick  up  bits  of  fat  from 
Showing  ata  the  cells  that  the  blood,  holding  it  uutil  it  is  wanted; 
secrete,  at  6  the  duct  that  Fig.  12.     These  cells  incidentally  form 

carries  away  the  secretion  j.       r  u*  i  •  r 

and  at  c  the  blood  ves-  ^  ^ort  of  cushiou  or  packmg  for  some 

sels  supplying  the  gland.      of    the    SOft    paits    of    the    body. 


Fig.  8.— Mus- 
cle CELLS 
FROM  THE 
WALL  OF  THE 
INTESTINE 


Fig.  9 — A  portion  of  a 


THE  LIVING  MATERIAL  OF  THE  BODY 


i: 


Although  there  is  much  diversity  in  the  forms  of  cells  in 
the  body,  each  tissue  is  made  of  only  a  single  kind  which 
does  a  single  kind  of  work.  The  size  of  cells  varies  widely. 
Some  of  the  smaller  cells  of  animals  are  not  more  than 
0.003  mm.  (^^  in.)  in 


i^\*^s®^:?^2*^»^^>srt*,^^, 


8  3  0  0 

diameter,  while  the  egg, 
which  is  essentially  a  cell, 
is  sometimes  several 
inches  in  diameter.  The 
majority  of  cells  in  most 
animals  vary  from  0.008 
mm.  to  0.01mm.  (-g-yVTr  to 
Yzww  i^-)  ^^  diameter; 
Fig.  13. 

Structure  of  Cells. — In 
recent  years  much  atten- 
tion has  been  paid  to  the 
more  minute  details  of 
cell  structure.  As  a  re- 
sult we  now  know  that 
all  cells,  while  differing 
in  outward  shape,  are  very  much  alike  in  their  internal 
organization.  Each  one  is  filled  with  a  semifluid  substance 
called  protoplasm,  and  this  protoplasm  is  the  part' of  the 
cell  which  is  really  alive.  Protoplasm  should  not  be  thought 
of  as  life  itself  but  it  is  the  only  material  in  which  life  is 
known  to  occur.  When  highly  magnified,  protoplasmic  fluid 
always  seems  to  contain  fine  granules,  or  it  may  look  like 
a  foam  of  extremely  small  bubbles  or  show  a  network 
of  excessively  minute  lines;  Fig.  14.  At  all  times,  if  the 
cells  under  observation  are  alive  and  are  not  too  much 
disturbed,  movement  of  the  protoplasm  is  evident.  No 
one  knows  the  cause  of  this  motion;  it  can  only  be 
accounted  for  by  saying  that  protoplasm  is  alive. 

Within  each  cell  is  a  specially  dense  bit  of  protoplasm  called 


Fig.  10. — Blood 

As  it  appears  when  put  on  a  glass  slide  and 
highly  magnified.  At  a  are  shown  red  cor- 
puscles and  at  6  white  corpuscles  or  leuco- 
cytes. 


18 


ADVANCED  PHYSIOLOGY 


the  nucleus.     This   nucleus  seems  to  be  the  center  of  the 

life  and  activity  of  the  whole  cell,  for  if  deprived  of  it  the 

cell  cannot  long  continue 
to  live.  There  are  other 
parts  of  the  cell,  as  is 
shown  in  Figure  14,  for 
the  cell  is  really  a  com- 
plicated bit  of  machinery. 
The  chemical  composi- 
tion of  protoplasm  is  not 
definitely  known,  but  cer- 
tain elements — carbon  (C), 
hydrogen  (H),  oxygen  (0), 
nitrogen  (N),  iron  (Fe), 
sulfur  (S),  calcium  (Ca) 
and  phosphorus  (P) — enter 
into  the  composition  of  all 
kinds  of  cell  protoplasm; 
other  elements  may  occur 
in  smaller  quantities. 

Protoplasm,  then, 
should  be  remembered  as 
the  only  living  substance 
in  the  body.  It  cannot 
live  long  without  a  nu- 
cleus, neither  can  a  nucleus 
live  without  the  support  of 
surrounding  protoplasm. 

The  living  protoplasm 
may  be  surrounded  by  a 
layer  of  greater  consistency. 
This  may  be  very  thick,  as 
in  cartilage  (Fig.  4) ;  it  may 

be  very  thin,  as  in  the  nerve  cell,  or  it  may  be  entirely  absent, 

as  in  the  white  blood  corpuscles;  Fig.  10. 


Fig.    II. — A  nerve  cell  or  neuron 

At  o  is  shown  the  cell  body;  b,  the  nu- 
cleus; c,  the  axon  of  a  nerve  fibre;  d, 
branching  of  the  fibre;  e,  muscle  fibres 
within  which  the  fibre  ends:  /,  a  node 
in  the  fibre.     (Barker) 


THE  LIVING  MATERIAL  OF  THE  BODY 


Id 


Fig.  12. — Fat  cells 

a,  representing  young  cells 
just  beginning  to  store  fat; 
h,  fully  developed  cells 
ailed  with  fat. 


We  may,  therefore,  define  a  cell  in  two  ways.  We  may 
say  that  it  is  one  of  the  unit  masses  of  which  the  tissues  are 
formed,  or  we  may  say  that  it  is  a 
bit  of  protoplasm  containing  a  nucleus 
and  generally  surrounded  by  a  cell  wall. 
In  either  case,  the  cell  is  the  unit  of 
life. 

The  Life  of  Cells. — There  are  cer- 
tain great  differences  between  this 
unit  of  living  matter  and  a  non-living 
thing.  Three  distinguishing  qualities 
belong  to  the  living  cell:  (1)  growth, 
(2)  self-repair,  (3)  increase  in  num- 
bers through  self-division.  These  powers  are  possessed  by 
no  other  material  in  the  world  save  protoplasm. 

The  growth  of  a  cell  is  in  all  cases  brought  about  by  material 
taken  in  from  the  outside.  In  the  human  body  this  material 
is  food,  which  after  di- 
gestion passes  into  the 
blood  and  is  then  taken 
in  by  the  cells.  This 
process  will  be  described 
more  fully  later.  In 
some  of  the  very  lowest 
organisms,  where  the 
whole  animal  is  a  single 
cell,  solid  particles  may  be  taken  into  the  cell  through 
definite  openings  or  "mouths";  Fig.  15.  In  others,  the 
cell  may  change  its  shape  so  as  to  wrap  itself  about  ths 
particle  to  be  taken  in.  But  even  in  these  instances  the  parti- 
cles must  be  dissolved  or  digested  before  they  can  be  built 
up  into  the  protoplasm  of  the  cells. 

A  machine  in  motion  wears  out,  and  the  worn  out  parts 
must  be  replaced.  Cells,  too,  wear  out  and  new  cells  must  be 
formed  or  new  protoplasm  is  required  tO  repair  the  old  ones. 


Fig.   13. — Showing  the  relative  size 

OF  A  pin  head  and  A  LARGE  SIZED  CELL 
The  small  dot  in  the  center  represents  the  cell. 


20 


ADVANCED  PHYSIOLOGY 


Xl^ Nuct 


Repair  and  growth  are  brougnt  about  by  one  and  the  same 
process,  the  difference  being  that  in  repair,  new  material  is 
added  only  as  fast  as  the  old  wears  away,  while  in  growth 
new  material  is  formed  in  excess  of  that  which  is  worn  out,, 
the  excess  constituting  the  growth. 

Cell  Division. —  Most  living  cells  have  the  power  of  self 
division  as  shown  in  Fig.  16.  This  results  in  two  cells  like  the 
original.  In  the  human  body,  however,  the  cells  do  not 
separate  from  each  other,  so  that  by  continued  repetition 
of  this  process  a  large  mass  of  cells 
is  produced. 

Reproduction. —  Every  animal  begins 
its  life  as  a  single  cell  —  an  egg.  This 
cell  repeatedly  divides,  the  many  cells 
remaining  attached  to  each  other. 
Thus  the  growth  of  an  animal  to 
adult  size  is  not  due  to  the  growth  in 
size  of  the  individual  cells  making  up 
its  body  but  to  increase  in  their  number. 
The  cells  of  the  adult  are  not  materially 
larger  than  those  of  the  young.  In 
time  one  or  more  of  the  cells  from  the 
body  of  the  adult  may  be  set  apart  as 
eggs,  the  process  outhned  above  being 
started  over  again.  This  derivation 
of  new  individuals  from  single  cells  of 
a  preceding  one  is  called  reproduction. 

The  Cell  as  a  Unit.—  We  have  thus 
seen  that  the  body  is  made  of  organs, 
that  the  organs  are  made  of  tissues  and  that  the  tissues  are  made 
of  cells.  Is  it  possible  to  carry  this  division  further?  To  this 
question  we  must  reply  that,  so  far  as  yet  known,  the  cell  is 
the  final  unit.  It  is  true  that  the  cell  has  parts — cell  wall,  nucleus, 
cell  substances  etc. — ^but  no  one  of  them  can  live  by  itself, 
while  a  complete  cell  may  be  an  independent  body  and  live  an 


PI. 

...C.R. 
CL. 

Fig  14. — A  cell  showing 

ITS  INTERNAL  STRUC- 
TURE 

C.W.,  cell  wall;  C.L.,  cell 
liquid;  C.  R.,  cell  reticulum; 
Nuc,  nucleus;  Nucl.,  nucleo- 
lus; Ch.,  chromatin;  Cn., 
centrosome;  Vac.  vacuoles; 
^l.,  plastida  (pigment,  chloro- 
phyll, etc.);  F.  D.,  fat  drops 
(starch,  gum  etc.  may  be 
eimilarly  present  in  plant 
ceU). 


Fia.  15. — Showing  a    variety   op   animals,   each    op    which   is   a 

SINGLE    CELL    ClllGHLV    MAUiNlFlEU; 


^ 


ADVANCED  PHYSIOLOGY 


independent  life.  Although  our  own  bodies  are  composed  of 
many  millions  of  these  cells,  there  are  some  organisms  made 
up  of  one  cell  only.  These  are  usually  microscopic  and  are 
called  unicellular  animals  and  plants;  although  very  tiny, 
each  lives  an  independent  life.  Some  of  these  animals  are 
shown  in  Figure  15.  They  vary  in  shape  and  differ  in  struc- 
ture. Some  of  them  have  ''mouths";  others  simply  take 
their  food  in  at  any  part  of  the  body  by  allowing  their  pro- 
toplasm to  flow  around  it.  Some  of  them  have  organs  for 
locomotion,  others  do  not.  Some  have  shells,  while  others 
have  no  covering  at  all.  But  each  is  a  single  cell,  and  each 
ijarries  out  its  own  life  processes,  such  as  respiration,  secretion 


Fig.  16. — Showing  the  method  op  cell  division 

and  multiplication.  The  cell  cannot  be  subdivided  into 
smaller  units  which  would  be  able  to  sustain  independent 
life. 

Since  such  cells  are  the  simplest  parts  into  which  living 
matter  can  be  divided,  we  may  call  them  the  units  of  life 
and  may  regard  our  bodies  as  a  combination  of  a  large  num- 
ber of  such  units,  considering  the  life  of  the  whole  body 
as  the  sum  of  the  lives   of  its   different   cells.     We  should 


THE  LIVING  MATERIAL  OF  THE  BODY  23 

constantly  remember  that  it  is  really  the  cells  which  are  the 
active,  living  parts.  The  combined  lives  of  all  these  millions 
of  cells  make  the  life  of  the  whole,  much  as  the  combined  lives 
of  the  persons  within  a  city  make  up  its  life. 

UNICELLULAR  AND  MULTICELLULAR  ANIMALS 

As  we  have  seen,  some  animals  are  composed  of  a  single 
cell.  But  this  cell  is  able  to  carry  on  all  the  functions  of  life : 
it  feeds,  digests,  respires,  moves,  multiplies  and  performs  all 
the  necessary  duties  of  complete,  individual  life.  In  our  own 
bodies  there  are  many  cells,  but  each  is  not  capable  of  carrying 
on  all  the  functions  of  life,  and  if  separated  from  the  others, 
would  die.  Each  is  able  to  do  primarily  only  one  thing; 
hence  each  is  dependent  upon  the  others. 

It  may  be  asked  why  we  should  have  so  many  kinds  of 
cells  in  our  bodies,  and  why  with  us,  too,  one  kind  of  cell 
could  not  serve  all  purposes.  The  answer  is  easy  to  give. 
A  hermit  can  himself  do  everything  needful  to  support 
his  life:  he  can  prepare  his  own  food,  make  his  own  clothes 
and  build  his  own  shelter.  But  he  can  do  this  only  be- 
cause he  lives  very  simply.  When  a  family  lives  alone  on 
the  frontier  the  members  divide  the  work  among  themselves, 
the  husband  doing  the  work  out  of  doors,  the  wife  that 
indoors  and  the  children  contributing  their  different  shares. 
When  several  families  come  together,  it  will  be  found  that 
some  members  of  the  community  are  more  skillful  in 
building  houses,  others  in  making  shoes,  others  in  dress- 
making, still  others  in  cooking  and  so  on;  so  the  people 
agree  to  divide  their  tasks  and  share  the  results  of  their  work. 
In  this  way  they  may  have  better  houses,  better  shoes,  better 
clothing  and  better  food  than  before,  because  each  man  does 
what  he  can  do  best.  As  the  community  grows  this  divi- 
sion  of  labor  becomes  extended  until,  in  a  large  city,  each 
person  does  only  a  very  small  part  of  the  work  necessary 
to  supply  him  with  the  things  he  needs.    But  he  can  do  his 


24 


ADVANCED  PHYSIOLOGY 


own  work  well  because  he  has  only  one  thing  to  do.  The 
life  of  a  city  is  of  much  higher  grade  than  that  of  a  pioneer 
family;  its  population  has  many  more  luxuries  and  ac- 
complishes much  more,  all  because  of  this  division  of  labor. 
The  people  become  more  and  more 
dependent  upon  each  other,  but 
for  just  that  reason  they  are  better 
served. 

So  it  is  among  organisms.  Where  one 
cell  does  everything,  the  life  is  simple 
and  on  a  very  low  scale.  Each  cell  can 
feed  itself  and  perform  all  the  necessary 
functions,  but  the  whole  life  is  only  one 
of  growth  and  reproduction.  As  the 
cells  become  more  abundant,  they  also 
become  unlike.  Each  takes  upon  itself 
certain  duties,  each  contributes  to  the 
good  of  the  other  cells,  and  each  receives 
aid  from  the  others.  In  Figure  17,  for 
example,  we  have  a  simple  animal  in 
which  two  kinds  of  cells  are  shown. 
Those  in  the  center  take  care  of  the 
digestion  of  food,  while  those  on  the 
outside  protect  the  animal  from  ex- 
ternal injuries.  The  entire  organism 
is  thus  much  better  served  than  it 
would  be  if  each  cell  had  all  the 
varied  duties  to  perform.  The  life  of 
any  animal  is  the  sum  of  the  lives 
of  its  cells,  and  with  many  kinds  of 
cells  all  working  together  for  a  common  good,  a  higher 
grade  of  activity  is  produced  than  with  each  working  for 
itself  alone.  Division  of  labor  goes  hand  in  hand  with  a 
rise  in  the  scale  of  accomplishment  and  results  in  a  superior 
type  of  life. 


Fig.  17. — A  multicel- 
lular ANIMAL  (Hy- 
dra) 

Showing  its  body  to  be 
made  of  many  cells  that 
are  not  all  alike,  B.base 
for  attachment ;  M, 
mouth;  DC,  digestive 
cavity. 


CHAPTER  II 
CHEMICAL  COMPOSITION  OF  THE  BODY 

Everyone  feels  that  he  knows  the  difference  between  an 
object  that  is  ahve  and  one  that  is  not  ahve;  and  certainly 
there  is  no  difficulty  in  distinguishing  between  them  when  we 
are  considering  such  things  as  dogs  and  stones.  But  how  can 
we  tell  whether  or  not  a  dried  pea  is  alive?  We  might  find 
out,  perhaps,  by  planting  it.  If  it  sprouted,  we  should  know 
that  it  had  life,  but  we  could  not  tell  by  its  appearance  nor 
by  pulling  it  to  pieces. 

When  it  proves  impossible  to  tell  the  nature  of  a  material 
from  surface  examination  or  by  dissection,  the  chemist  is 
usually  called  in  to  settle  the  question.  It  would  be  natural 
to  suppose  that  living  and  non-living  bodies  are  made  of 
different  chemical  materials;  that  the  living  body  contains 
some  hidden,  secret  thing  which  the  non-living  lacks. 

ELEMENTS 

For  a  century  or  more  chemists  have  been  at  work  trying 
to  divide  things  into  the  simple  materials  of  which  they 
are  made.  Those  simple  materials  which  cannot  be  further 
divided  are  called  elements.  Out  of  one  or  more  of  them,  all 
the  various  kinds  of  material  in  the  world  are  made.  Rather 
to  our  surprise  we  find  that  there  are  but  a  small  number 
of  elements,  only  about  eighty-one  being  known  of  which 
less  than  twenty  make  up  most  of  the  common  things. 
This  seems  a  remarkably  small  number  until  we  learn  how 
many  different   things   can  be  made    from  the  same  ele- 

25 


26 


ADVANCED  PHYSIOLOGY 


merits.  Think,  for  example,  of  sugar,  alcohol,  glycerine, 
kerosene  oil,  starch,  benzine,  paraffin  and  fat.  How  unlike 
they  are!  In  spite  of  their  apparent  differences,  all  these 
substances  are  made  of  carbon,  hydrogen  and  oxygen;  each 
one  contains  these  three  and  nothing  more;  they  differ  only 
in  the  various  proportions  of  the  elements.  In  a  similar 
way,  by  varying  the  amount  of  each  element  put  into 
any  combination,  all  the  different  substances  in  the  world 
are  made  from  the  eighty-one  elements.  This  is  true 
of  animals  as  well  as  of  all  other  material  things.  The  fact 
that  the  body  weighs  just  as  much  immediately  after  as  it 
does  before  death,  shows  that  no  substance  is  lost  at  death. 
There  is  really  no  difference  between  dead-weight  and  live- 
weight;  clearly  then  the  same  elements  enter  into  Uving  and 
dead  bodies. 


Oxt/qen 


Fig.  18. — Diagram  illustrating  the  relative  amounts  of  some  of 

THE    elements    IN    THE    CHEMICAL    COMPOSITION  OF  THE  BODY. 


CHEMICAL  COMPOSITION  OF  THE  BODY 


27 


Water,  for  example,  as  it  leaves  the  body  as  perspiration, 
is  made  of  hydrogen  and  oxygen,  the  same  as  water  from  a 
faucet.  The  juices  formed  in  the  stomach  are  partly  made 
of  hydrochloric  acid,  the  same  as  that  used  in  various  manu- 
facturing processes.  Much  of  the  material  in  bones  is  lime; 
some  of  the  material  in  blood  is  iron,  and  it  becomes  red  when 
mixed  with  oxygen,  the  same  as  iron  does  when  it  rusts. 
Salt  is  easily  noticed  in  perspiration  and  tears,  and  has  the 
same  composition  as  table  salt. 

!  Living  matter  contains  but  a  small  number  of  the  seventy- 
seven  elements  referred  to  above;  those  commonest  in  the 
body  are  carbon,  hydrogen,  oxygen,  nitrogen,  calcium,  phos- 
phorus, sulfur,  sodium,  chlorine,  fluorine,  potassium  and 
iron.  The  following  table  shows  approximately  the  per- 
centage in   which  each  occurs: 

CHEMICAL  COMPOSITION  OF  THE  BODY 


Elements 

Sym- 
bol 

Percent- 
age 

Elements 

Sym- 
bol 

Percent- 
age 

Oxygen 

0 

72 

Chlorine 

CI 

.085 

Carbon 

C 

13.2 

Fluorine 

F 

.08 

Hydrogen 

H 

9.1 

Potassium 

K 

.026 

Nitrogen 

N 

2.5 

Iron 

i^e 

.01 

Calcium 

Ca 

.25 

Magnesium 

Mg 

.0012 

Phosphorus 

P 

.15 

Silicon 

Si 

.0002 

Sulfur 

S 

.02 

Copper,Lead  and 

Sodium 

Na 

.3 

Aluminium 
in  very  small 
quantities 

These  are  the  same  chemical  elements  which  we  should 
find  if  we  analyzed  materials  all  around  us  in  nature;  e.g. 
air,  water,  soil  or  rocks.  The  Hving  body  is  thus  constructed 
of  the  same  materials  as  are  found  in  non-living,  inanimate 
bodies.     But  there  must  be  some  difference.    What  is  it? 


28  ADVANCED  PHYSIOLOGY 


THE  CHIEF  CHEMICAL  COMPOUNDS  IN  THE  BODY 

If  the  materials  used  in  building  a  city  block  were  chemi- 
cally analyzed,  many  of  the  elements  found  would  be  the 
same  as  those  present  in  the  body.  But  when  we  talk  about 
the  construction  of  a  building,  we  never  mention  the  chemi- 
cal elements  of  which  it  is  composed;  we  speak  rather  of 
the  compounds  of  these  elements.  Beams,  piping,  windows, 
chimneys,  furnaces,  flooring  and  doors  are  all  parts  of  the 
building,  but  they  can  be  roughly  classified  as  made  of  wood, 
iron,  brick  or  stone.  Similarly,  in  speaking  of  our  bodies, 
mention  is  seldom  made  of  the  chemical  elements  in  them, 
but  of  the  combinations  in  which  the  elements  most  fre- 
quently occur. 

There  are  three  compounds  that  are  of  supreme  import- 
ance in  living  animals.  They  constitute  almost  all  the 
essential  materials  in  our  bodies.  Since  they  are  also  the  prin- 
cipal constituents  of  our  foods,  they  are  called  food  stuffs. 
These  compounds  are:  (1)  proteids,  (2)  carbohydrates  and 
(3)  fats.    Water  and  salts  are  also  necessary. 

Proteids  (Albumen,  Myosin,  Gluten,  Casein,  Legumen,Fibrin). 
— Proteid  is  made  up  chiefly  of  four  elements:  carbon,  hydrogen, 
oxygen  and  nitrogen,  though  sulfur  and  phosphorus  are 
present  in  small  quantities.  Proteid  occurs  in  all  animal  and 
vegetable  organisms.  For  example,  in  the  human  body 
proteid  comprises  38.3%  of  the  lens  of  the  eye,  16%  of  the 
muscles,  12%  of  the  liver,  9%  of  the  blood.  These  percent- 
ages are  not  so  small  as  they  seem,  since  the  greater  part 
of  all  tissues  is  water.  The  human  body,  taken  as  a  whole, 
is  nearly  67%  water,  and  the  proteids  form  a  large  proportion 
of  the  rest. 

Proteids  as  Tissue  Builders. — The  proteid  which  the  body 
contains  must  either  be  obtained  directly  in  foods  or  be  made 
from  them.     Now  the  body  is  quite  unable  to  make  proteid; 


CHEMICAL  COMPOSITION  OF  THE  BODY  29 

hence  it  follows  that  proteids  form  an  absolutely  necessary- 
part  of  our  food.  We  must  eat  a  sufficient  amount  of 
proteid  or  we  shall  starve,  no  matter  how  much  other  food 
we  eat.  Proteid  is  needed  in  all  the  working  parts  of  the 
body.  Muscle  and  blood  are  pre-eminently  active.  Perform- 
ing absolutely  vital  functions  every  moment  of  our  lives, 
they  are  constantly  exposed  to  "wear  and  tear"  and  unless 
they  were  repaired  would  become  exhausted  and  worn  out. 
The  body  must  have  new  proteid  for  repair  purposes  and  the 
proteid  must  be  provided  by  the  use  of  proteid-containing  food. 
This  food  may  be  obtained  from  many  sources.  Some 
proteids  come  from  animal  and  some  from  vegetable  materials. 
That  from  meats  is  called  myosin;  that  from  eggs  is  albumen; 
that  from  milk  is  casein;  that  from  wheat  is  gluten;  that 
from  beans  is  legumen.  But  although  differently  named  and 
differing  in  value  to  the  body,  all  these  forms  of  proteid  serve 
as  a  food  which  can  replace  and  repair  the  worn-out  parts  of 
the  body.  If  we  remember  that  proteids  alone  can  thus  re- 
place worn-out  tissue,  we  shall  understand  their  fundamental 
importance. 

One  naturally  and  correctly  feels  that  proteids  from  animal 
sources  are  probably  most  like  that  of  the  human  body,  and 
so  can  be  used  with  better  results.  Furthermore,  as  all  sub- 
stances taken  as  foods  must  be  masticated,  swallowed,  digested, 
absorbed  into  the  blood,  carried  over  the  body  and  then  re- 
ceived into  the  living  cells  and  made  a  part  of  the  body  sub- 
stance, it  is  easy  to  imagine  that  some  proteids  undergo  these 
changes  more  readily  than  others,  and  so  are  more  valuable. 

In  a  later  chapter  dealing  with  foods  the  differing  values 
of  various  proteids  will  be  discussed.  Some  kinds,  taken 
alone,  will  not  support  the  growth  of  an  animal  at  all;  others 
seem  to  furnish  every  needed  substance,  even  when  quite 
small  quantities  are  taken.  Very  extensive  and  expensive 
studies  have  been  made  in  recent  years  in  the  analysis  of  all 
kinds  of  proteids  and  other  food  substances,  together  with 


30  ADVANCED  PHYSIOLOGY 

their  digestibility  and  final  values.    Human  beings  have  been 
used  in  these  experiments  so  that  the  results  are  of  great  value. 

Proteids  as  Fuel. — To  keep  an  engine  running  it  is  not 
enough  that  it  be  kept  in  repair;  there  must  be  a  fire  in 
the  fire-box.  In  one  respect  the  body  differs  from  an  engine : 
while  the  iron  of  which  a  locomotive  is  made  cannot  be  used 
as  fuel,  the  proteids  of  which  the  body  is  made  can  be 
burned.  By  being  burned  we  mean  here,  united  with  oxygen, 
a  phenomenon  which  chemists  call  oxidation.  Foods  in  the 
body  unite  with  oxygen  and  this  may  be  called  ''  burning," 
though  the  oxidation  is  not  so  rapid  in  the  body  as  in  an 
actual  fire,  and  there  is,  of  course,  no  flame:  but  the  union 
with  oxygen  is  similar,  heat  is  developed  in  a  similar  manner 
and  the  final  results  are  much  alike.  Proteids  have  a  double 
value:  (1)  they  are  burned  in  the  body  and  (2)  they  build  up 
tissue.  When  all  the  proteid  eaten  is  not  needed  to  build  up 
or  to  repair  the  tissue,  the  rest  may  be  burned  to  furnish  heat 
and  force. 

In  using  proteids  for  fuel  there  is,  however,  one  disadvan- 
tage which  limits  their  value  as  food.  After  any  fuel  is 
burned,  certain  waste  products  always  remain.  When  a  fire 
burns  in  a  locomotive,  a  vast  amount  of  smoke  and  gas 
arises  and  passes  off  through  the  smoke-stack,  while  ashes  are 
left  to  be  raked  down  through  the  grate  and  thrown  away. 
The  fire  will  not  continue  to  burn  unless  these  waste  ashes 
and  gases  are  removed.  In  the  body,  too,  as  a  result  of  the 
burning,  gases  and  other  wastes  arise.  The  gases  pass  off 
readily  enough  through  the  lungs.  But  there  is  a  more 
troublesome  residue  that  corresponds  to  the  ashes.  We  have 
noticed  that  proteids  contain  some  of  the  chemical  element, 
nitrogen.  After  the  burning  of  the  proteid  in  the  body, 
this  nitrogen  becomes  a  waste  product  and  can  be  disposed 


CHEMICAL  COMPOSITION  OF  THE  BODY  31 

of  only  as  an  excretion  of  the  kidneys.  The  more  proteid 
we  burn  for  fuel,  the  more  of  this  waste  there  is,  and  hence 
the  greater  the  work  of  the  kidneys.  If,  therefore,  we  eat 
large  amounts  of  proteid,  the  kidneys  have  extra  work  to  do; 
indeed,  it  is  believed  that  some  kidney  troubles  are  produced 
or  at  least  aggravated  by  overtaxing  those  organs  from  the 
consumption  of  too  much  proteid. 

Nevertheless,  the  body  must  continue  to  burn  fuel  in 
order  to  keep  up  its  life;  it  can  no  more  live  without  burn- 
ing fuel  than  the  locomotive  can  run  without  its  fires.  If 
it  is  not  wise  to  burn  great  amounts  of  proteid,  what  can  the 
body  use  as  a  source  of  the  necessary  heat  and  power?  If 
there  is  some  kind  of  food  that  furnishes  the  required  energy 
without  leaving  behind  nitrogen  waste  materials,  it  will 
evidently  be  of  much  value.  There  are  two  such  classes 
of  foods:  carbohydrates  and  fats. 

Carbohydrates. — Although  starches  and  sugars  seem  very 
different,  they  are  really  much  alike  in  chemical  composition 
and  may  be  converted,  the  one  into  the  other.  It  is  especially 
easy  to  change  starch  into  sugar.  The  similarity  in  their 
chemical  formulae  is  very  noticeable.  Fruit  sugar  is 
Ce  Hi2  Oe;  starch  is  Ce  Hio  O5.  Starches  are  always  turned 
into  sugars  and  dissolved  before  they  are  taken  from  the 
intestine  into  the  blood.  From  the  blood  vessels  the  sugars 
penetrate  into  all  the  tissues  and  are  soon  very  widely 
distributed. 

Sugars  and  starches  of  various  sorts  are  so  commonly  seen 
that  one  should  be  warned  against  thinking  of  these  sub- 
stances, after  their  assimilation  into  the  body,  as  having  their 
usual  appearance.  Both  may  be  present  in  solid  or  crystalline 
form  in  the  cells  of  plant  leaves,  stems  or  roots;  but  not  so  in 
the  cells  of  any  kind  of  animal.  The  nearest  to  it  is  a  sub- 
stance found  especially  in  the  cells  of  the  liver  and  in  muscles 
and  called  glycogen.     The  chemical  formula  of  glycogen  is  the 


32  ADVANCED   PHYSIOLOGY 

same  as  that  of  starch  (C6Hio05)n,  though  the  two  substances 
have  little  else  in  common.  Glycogen,  too,  varies  much  in  the 
amount  stored  up  when  an  excess  of  sugar  is  eaten,  and  dis- 
appears when  one  is  hungry. 

Fats. — Tallow,  lard,  cream,  olive  oil  etc.  furnish  another 
fuel  that  can  be  burned  without  giving  a  nitrogen  waste. 
These  fats  are  derived  from  both  animal  and  vegetable 
foods  and  though  made  of  the  same  elements  as  carbohy- 
drates (C,  O  and  H),  they  are  more  complex.  Fat  is  plentiful 
in  the  body  in  both  fluid  and  semi-fluid  condition.  It  is 
absorbed  by  the  blood  from  the  intestine  in  a  fluid  condition, 
is  carried  around  the  body  in  the  blood  and  is  eventually 
taken  from  it   and  deposited  in  various  parts  of  the  body. 

Fat  occurs  in  masses  among  the  muscles  and  just  beneath 
the  skin;  it  forms  a  cushion  for  the  eyeballs  at  the  bottom 
of  the  eye  sockets;  it  is  present  among  the  folds  of  the 
intestine;  it  fills  up  certain  crevices  in  the  exterior  of  the 
heart  muscle  and  is  deposited  in  the  central  marrow  of  the 
larger  bones. 

Evidence  of  these  facts  we  have  all  seen  many  times  in  food 
markets  where  meats  are  displayed.  No  meat  is  mingled 
with  so  much  fat  as  pork;  hogs  have  famously  large  appe- 
tites and,  at  the  same  time,  sluggish  habits.  A  result  of  this 
is  that  only  partial  use  of  the  fats  is  made  for  energy  or  heat 
production,  thus  leaving  excessive  fat  to  be  stored.  A  farmer 
rather  easily  controls  the  degree  of  fatness  of  horses,  cattle, 
chickens,  and  other  animals  by  attention  to  their  food  and 
exercise;  and  their  food  does  not  necessarily  contain  fatty 
substances,  for  many  animals  become  fleshy  though  eating 
nothing  but  the  proteids  and  carbohydrates  in  hay  and  grain. 

Uses  of  Carbohydrates  and  Fats. — The  body  must  at  all 
times  be  kept  warm  and  is  constantly  using  power  in 
muscular  activity.  Heat  and  power  may  roughly  be  said  to 
constitute  energy,  and  in  order  to  live  the  body  must  have  not 


CHEMICAL  COMPOSITION  OF  THE  BODY  33 

only  material  for  growth  and  repair,  but  also  a  supply  of 
energy. 

Fat  is  a  form  in  which  the  body  frequently  stores  fuel 
food  for  future  uses.  If  the  body  has  an  abundance  of  food 
at  one  time,  it  need  not  all  be  used  immediately  but  may  be 
laid  aside  as  fat,  to  be  called  into  use  at  some  later  time 
when  the  body  may  not  be  able  to  secure  or  to  take  up  the 
necessary  amount  of  food. 

After  a  long  sickness  a  patient's  eyes  are  likely  to  be 
sunken  and  the  ribs  to  show  through  the  skin.  This  is 
due  to  the  fact  that  during  his  illness  he  has  not  been  able 
properly  to  digest  and  assimilate  food,  and  has  been  caUing 
upon  the  stores  of  fat  in  his  body  to  support  life  and  furnish 
him   Vv^ith   warmth   and  energy. 

A  tallow  candle  is  made  of  fat  and  when  it  burns,  gives 
out  heat.  The  Eskimo  can  warm  his  hands  by  holding  them 
over  the  burning  candle;  but  he  prefers  to  eat  the  candle  and 
let  it  warm  his  body  through  internal  oxidation.  In  this  way 
he  does  not  lose  any  of  the  heat.  It  would  be  perfectly 
possible,  though  expensive,  to  warm  our  houses  by  burning 
lard,  olive  oil  or  butter  in  our  furnaces.  So,  too,  we  might 
burn  starches  or  sugars  for  the  same  purpose,  or  might  run 
an  engine  with  the  force  they  would  furnish  when  burning. 
Whenever  these  substances  are  oxidized,  they  liberate  much 
energy  and  if  they  are  oxidized  in  the  body,  they  liberate 
this  heat  and  force  within  it. 

Carbohydrates  and  fats  do  not,  however,  yield  equal 
amounts  of  energy  to  the  body,  the  carbohydrates  giving 
us,  weight  for  weight,  only  about  half  as  much  as  the  fats. 
Both  are  composed  of  the  same  elements,  carbon,  oxygen  and 
hydrogen,  and  it  is  natural  as  well  as  quite  worth  while  to 
ask  why  one  yields  so  much  more  than  the  other.  The 
answer  Ues  in  the  relative  amounts  of  carbon  which  these 
foods  contain;  the  chemical  formula  for  starch  is  CeHioOs; 
for  sugar,  C6H12O6;  for  fat,  C61H104O9.    Now,  in  the  changes 


34  ADVANCED  PHYSIOLOGY 

which  these  undergo  in  the  body  much  of  the  hydrogen 
may  combine  with  the  oxygen  to  form  water,  H2O,  while 
the  carbon  also  unites  with  oxygen  to  form  carbon  dioxid, 
CO2.  It  is  this  combining  with  oxygen,  this  oxidation  of 
materials,  which  results  in  heat,  just  as  it  is  when  the 
carbon  in  burning  wood  unites  with  oxygen  of  the  air,  and 
gives  off  heat  in  making  the  combination. 

As  will  be  noticed  from  the  above  formulae,  fat  contains 
fifty-one  parts  of  carbon,  while  sugar  contains  only  six.  Heat 
is  produced  when  the  carbon  combines  with  oxygen,  as  we 
have  said.  In  sugar  the  carbon  already  has  six  parts  of 
oxygen  combined  with  it  and  cannot  combine  with  very  much 
more.  In  fat,  however,  there  are  fifty-one  parts  of  carbon, 
and  only  nine  parts  of  oxygen  combined  with  it.  In  fat  there 
is  therefore  a  much  larger  amount  of  carbon  which  can  be  com- 
bined with  the  oxygen  of  the  air  than  there  is  in  sugar;  when 
fat  is  burned  there  is  a  large  amount  of  oxidation  and  hence 
a  far  greater  amount  of  heat  given  off.  Indeed,  fat  furnishes 
a  larger  amount  of  heat  than  any  other  food. 

Thus  carbohydrates  and  fats  furnish  us  with  a  quick  and 
profitable  source  of  energy.  It  must  be  clearly  understood, 
however,  that  neither  of  them  is  of  any  value  in  tissue 
building.  Neither  muscle  nor  brain  nor  gland  nor  any 
other  active  tissue  can  be  made  or  even  repaired  by  them. 

Gelatin. — Most  meat  foods  contain  another  material  known 
as  gelatin,  which  in  its  refined  form  causes  the  hardening  of 
most  of  our  table  jellies.  It  is  obtained  from  connective 
tissues  (see  page  13)  by  boiling.  In  its  chemical  nature  it 
resembles  proteid,  but  it  will  not  take  the  place  of  proteid 
in  tissue  building.  It  may  be  used  by  the  body  as  a  source 
of  energy  and  hence  has  much  the  same  function  as  carbo- 
hydrates. In  eating  jellies  one  is  likely  to  be  deceived  into 
thinking  that  he  is  eating  more  than  he  is,  since  they  contain 
much  water  and  are  bulky,  considering  the  small  amount  of 
aetual  food  in  them. 


CHEMICAL  COMPOSITION  OF  THE  BODY  35 

METABOLISM 

All  the  materials  of  which  living  bodies  are  composed  come 
from  the  soil  and  from  the  air.  All  vegetable  foods  surely 
come  from  these  sources;  animals  eat  plants  or  eat 
other  animals  which,  in  turn,  live  on  plants.  After  being 
taken  into  the  body  the  foods  go  through  certain  changes,  the 
final  result  of  which  is  that  part  of  the  food,  at  least,  is 
transformed  into  living  tissues.  These  changes  constitute 
what  is  generally  spoken  of  as  a  "  building  up  "  process, 
which  means  that  complex  substances  are  made  of  simple 
ones.  After  these  tissues  have  severally  fulfilled  their 
functions,  serving  as  muscle,  brain,  fat,  bone  or  gland,  as  the 
case  may  be,  they  gradually  wear  out;  as  this  occurs  they 
are  "  broken  down "  from  their  complex  condition  into 
simple  forms  again. 

In  living  matter,  there  occur  two  types  of  changes — a 
building  up,  or  anabolism,  and  a  breaking  down,  or  kata- 
bolism.  As  a  result  of  this  breaking  down  process  the  sub- 
stances which  have  been  alive  and  have  acted  at  the  bidding 
of  our  wills  become  again  inactive  and  non-living.  Gradually 
all  parts  of  our  bodies — heart,  brain  and  everything  else — 
become  once  more  a  part  of  the  soil  and  air,  just  as  they  were 
before  they  were  first  taken  up  by  plants.  The  changes  are 
long  and  complex.  Some  take  place  in  the  body  and  some 
outside  the  body,  for  materials  are  sometimes  excreted  before 
they  are  completely  broken  down.  The  changes  that  take 
place  in  the  body,  the  building  up  and  the  breaking  down 
taken  together,  are  spoken  of  as  metabolism.  Metabolism 
is  thus  a  name  for  the  chemical  changes  which  are  taking 
place  in  living  tissues. 

Many  factors  combine  to  regulate  each  of  these  pro- 
cesses. Katabolism  (destructive  change),  for  instance,  is 
increased  by  excessive  work;  by  poor  nuirition,  by  loss  of 


36  ADVANCED  PHYSIOLOGY 

sleep,  by  nervousness,  by  various  diseases  and  by  the  action 
of  certain  poisons  and  drugs,  such  as  opium,  chloral  and 
alcohol.  It  seems  strange  that  men  should  consciously  persist 
in  the  use  of  some  foods,  and  especially  some  drinks,  which 
inevitably  bring  about  this  increased  katabolism  in  im- 
portant organs;  that  they  should  continually  expose  them- 
selves to  weakening  processes  which  the  building  up  processes 
can  counterbalance  with  difficulty,  if  at  all. 

Growth. — The  body  is  evidently  a  very  active  center  into 
which  large  amounts  of  material  are  constantly  entering  in 
the  form  of  food,  drink  and  air,  and  from  which,  at  the 
same  time,  large  amounts  are  constantly  being  eliminated. 
Body  substance  is  being  constructed  and  destroyed  at  the 
same  time,  and  if  these  two  processes  are  going  on  at  the 
same  rate,  the  body  neither  increases  nor  diminishes  either 
in  weight  or  efficiency.  Such  a  condition  is  commonly 
spoken  of  as  one  of  metabolic  equilibrium. 

If,  on  the  other  hand,  the  destructive  processes  take 
place  more  rapidly  than  those  of  construction,  the  body  will 
lose  in  weight  or  efficiency,  and  if  this  condition  of  things 
continues  long  enough,  death  must  result.  When  the  con- 
structive processes  in  the  body  go  on  faster  than  the  de- 
structive or  wearing  away  processes,  the  result  is  an 
crease  in  weight  or  in  efficiency.  The  growth  of  the  bod] 
then,  is  the  result  of  the  excess  of  constructive  changes  ov^ 
destructive  changes. 

Anabolism  exceeds  katabolism  during  childhood  and  earj 
youth;    but    after  adult    life    is    reached,     under    ordinal 
circumstances  the  body  maintains  itself  in  metabolic  eqi 
librium.     This  latter  condition  constitutes  what  is  general! 
spoken  of  as  healthy  the  maintenance  of  which  should  be  a 
matter  of  careful,  serious  attention  as  long  as  life  lasts. 


CHAPTER  III 
FOODS   AND   FOOD   HABITS 

It  is  important  for  us  to  know  the  real  nutritive  value 
of  the  foods  that  we  commonly  eat.  In  this  study  it 
should  be  constantly  borne  in  mind  that  for  the  proper 
support  of  life  we  must  have  a  considerable  amount  of  pro- 
teid  since  this  material  alone  builds  up  the  tissues  of  the 
body.  Carbohydrates  and  fats  can  be  used  only  as  sources 
of  heat  and  force. 

Scientific  men  who  spend  their  time  studying  the  fossils 
of  animals  which  lived  ages  ago,  and  which  are  known  now 
only  by  their  imperfectly  preserved  skeletons,  tell  us  that 
they  can  determine  what  the  animal  ate  and  much  about 
the  rest  of  its  body  if  they  can  find  the  teeth.  We  cannot 
say  what  it  was  originally  intended  that  man  should  eat; 
certainly  it  was  not  the  kind  of  food  which  he  eats  now,  for 
many  of  our  foods  are  recently  discovered.  But  we  can  say 
that  his  teeth  are  adapted  for  cutting,  tearing  and  grinding, 
and  that  his  habits  are  omnivorous;  i.  e.  he  eats  almost 
all  kinds  of  foods.  In  the  preparation  of  foods,  he  has  con- 
trived methods  which  change  their  flavor,  their  appearance 
and  their  smell.  He  is  able  to  have  summer  foods  in  winter, 
and  spring  foods  in  the  autumn.  Since  he  eats  such  a  variety 
of  things  under  such  different  forms,  the  queries  naturally 
arise:  W.hich  are  the  best  of  these  foods?  Which  kinds 
are  most  easily  digested?      Which  yield  the  most  nutriment? 

FOOD    HABITS 

We  sometimes  think  that  our  foods  are  rather  monoto- 
nous and  wish  some  new  kinds  might  be  found;    yet  it  is 

37 


38  ADVANCED  PHYSIOLOGY 

interesting  to  note  the  great  variety  of  foods  on  which  people 
live.  Americans  do  not  eat  the  same  foods  as  Japanese, 
and  yet  one  nation  thrives  as  well  as  the  other.  The  Spar- 
tans subsisted  mainly  on  dried  fruits  and  honey;  the  Chinese 
employ  rice  as  a  staple  article  of  diet,  and  many  of  the  Italians 
make  a  similar  use  of  chestnuts.  White  caterpillars,  seal 
or  whale  blubber,  tallow  candles,  leather,  shark's  fins,  grass- 
hoppers, earthworms,  deer's  sinews,  dogs,  cats,  rats,  are 
choice  articles  of  diet  with  different  people.  These  seem  odd 
preferences,  but  are  they  more  so  than  oysters  or  crabs  in 
their  shells,  and  shrimps  or  frozen  cream,  all  of  which  are 
common  with  us? 

The  fact  is  that  with  the  exception  of  the  woody  tissues 
of  plants,  almost  any  part  of  an  animal  or  plant  may  yield 
nourishment,  and  under  some  conditions  serve  as  food. 
From  an  endless  list,  our  selectioix  depends  chiefly  upon 
the  customs  of  the  community  in  which  we  live,  on  our 
taste  and  on  the  cost.  A  person  is  always  mistaken  when 
he  thinks  that  any  particular  kind  of  food  is  a  necessity. 
We  can  all  adapt  ourselves  to  a  wide  variety  and  it  is  best  to 
become  accustomed  to  the  kinds  of  food  most  conveniently 
obtained  under  the  ordinary  conditions  of  living  in  one's  own 
community. 

Some  foods  are  more  useful  than  others;  some  are  ex- 
pensive, some  difficult  to  digest  and  some  dangerous  to 
health.  It  is  fortunate  for  the  majority  of  people  that  the 
expensive  foods  are  really  no  better  than  the  cheaper  ones; 
indeed,  expensive  kinds  are  usually  rich  foods  which,  in 
the  end,  are  almost  sure  to  produce  digestive  troubles. 

THE   VALUE    OF    DIFFERENT   FOODS 

Many  things  have  to  be  considered  in  determining  what 
it  is  best  to  buy  for  the  table.  Certain  very  good  foods  do 
not  grow  in  some  parts  of  the  country,  and  this  makes  them 
expensive.      Other    foods   are    expensive    even    where    they 


FOODS  AND  FOOD  HABITS 


39 


2:;row  because  of  the  cost  of  raising  and  refining  them.  We 
ike  to  have  them  on  the  table  because  they  are  ''choice." 
Does  their  nutritive  value,  however,  compensate  for  the 
Additional  cost?  Some  foods  are  attractive  but  not  nutri- 
:ious,  and  vice  versa.  To-day  people  are  engaged  in  a  wide 
variety  of  occupations;  their  bodies  are  worn  out  in  dif- 
erent  ways;  then,  too,  some  people  can  afford  to  pay  twice 
IS  much,  perhaps  ten  times  as  much  as  others  for  their  food. 
In  considering  these  matters,  we  will  take  them  up  from 
:he  standpoint  of  the  three  primary  food  stuffs. 

Proteid  Yielding  Foods. — 

PERCENTAGE  OF  PROTEID  IN  SOME  COMMON  FOODS 


Cheese,  skim 

Poultry 

Egg,  white 

Beef,  lean 

Mutton,  lean 

Veal 

Salmon 

Egg,  yolk 

Beef,  fat 

Mutton,  fat 

Milk 

Peas  and  Beans 

Flour 

Bread 

44.8 

21. 

20.4 

19.3 

18.3 

16.5 

16.1 

16. 

14.8 

12.4 

3. 
24. 
10.8 

8.1 

— 

From  this  table  it  will  be  seen  that  animal  foods,  in  gen- 
eral, furnish  the  largest  amounts  of  proteid.  Whenever  we 
3at  meat,  eggs,  milk  or  cheese,  we  get  a  great  deal  of  this 
food  stuff.  We  learn,  too,  that  though  we  may  eat  the  same 
1  mount  of  food  each  day,  we  do  not  by  any  means  always 
3at  the  same  amount  of  proteid.  Fat  pork  often  contains 
much  less  than  half  the  proteid  per  pound  that  lean  beef 


40 


ADVANCED  PHYSIOLOGY 


does,  and  not  more  than  three-fifths  as  much  as  fat  beef. 
Nevertheless,  we  eat  one  kind  of  meat  for  dinner  one  day 
and  another  the  next,  and  since  we  eat  about  the  same 
amount  of  each,  we  certainly  obtain  more  proteid  food  with 
some  meals  than  with  others. 

Demonstration. — Boil  an  egg  for  ten  minutes  and  remove  the  shell. 
Cut  in  halves  to  show  the  coagulated  albumen  and  the  yolk. 

The  amounts  of  proteid  in  different  vegetables  also  vary 
greatly:   peas    and    beans    furnish    an    exceptionally    large 


Fig.  19. — Graphic  representation  of  the  food  values  of  bread,  beef 

AND  eggs 

Fats  are  shown  in  black,  carbohydrates  in  horizontal  dotted  lines,  and  proteids  in 
vertical  dotted  lines.     Other  parts  are  water. 

amount  of  proteid;  cereals,  such  as  wheat,  oatmeal  and  corn 
meal  have  less,  but  still  contain  a  large  quantity;  vege- 
tables and  fruits,  such  as  cabbages,  lettuce,  tomatoes 
and  asparagus  hold  very  small  amounts,  yet  we  often 
substitute  one  of  these  foods  for  another.  These  vege- 
tables and  fruits  are  useful  as  promoters  of  digestion,  or 
because  they  have  a  pleasant  flavor,  but  they  must  not  be 


FOODS  AND  FOOD  HABITS 


41 


looked  upon   as  furnishing  any  great  amount  of  real  food. 

It  is  clear,  then,  that  the  common  kinds  of  foods  differ 

much  in  their  nutritive  value,  and  though  ordinarily  we  do 

Wheat 

Turnip 


Fig. 


20. — Showing  the  nutritive  values  of  different  foods 

The  shading   as  in   Figure    19. 


not  think  of  this  fact,  we  should  bear  it  in  mind  if  we  would 
properly  regulate  our  diet.  So  far  as  proteid  is  concerned, 
this  is  graphically  shown  by  Figures  19  and  20. 

Relative  Expense  of  Proteid  Foods. — Few  things  contribute 
more  to  health  and  happiness  than  intelligence  in  choosing 
foods.  In  the  selection  each  person  will  be  guided  by  a  num- 
l)er  of  considerations.  Some  nutritious  foods  can  be  obtained 
at  much  smaller  cost  than  others;  for  instance,  a  quarter  of  a 
})Ound  of  cheese  usually  contains  as  much  proteid  as  half  a 
pound  of  lean  meat  or  three-quarters  of  a  pound  of  fat  meat; 
half  a  pound  of  beans  or  bread  contains  as  much  of  the  needed 
proteid  as  a  pound  of  fatty  meat,  though  its  cost  is  much 
'ess;  Fig.  19.  Skimmed  milk  contains  as  much  proteid  as  whole 
milk,  the  cream  being  chiefly  fat  and  in  some  respects  of 


li 


42 


ADVANCED  PHYSIOLOGY 


much  less  value  as  nutriment  than  the  casein  in  the  skimmed 
milk.  Vegetables,  in  general,  such  as  cabbage  and  lettuce, 
contain  extremely  little  nourishment  of  any  kind.  As  a  rule, 
it  is  better  to  purchase  foods  which  have  large  quantities  of 
the  necessary  substances  in  them  than  those  which  have 
small  amounts.  If  we  should  eat  enough  of  the  latter  kind, 
we  could,  of  course,  obtain  all  the  food  we  need;  but  it 
would  compel  the  digestive  organs  to  do  a  quite  unnecessary 
amount  of  work. 

The  following  list,  giving  the  amount  of  proteid  which 
can  be  bought  in  different  forms  for  ten  cents,  will  be  of  value 
as  a  guide  to  an  economical  purchase  of  table  supplies. 

AMOUNT  OF  PROTEID  PURCHASABLE  FOR  TEN  CENTS 


Beans 

Oatmeal 

Wheat  flour 

Corn  meal 

Cheese 

Wheat  bread 

Potatoes 

Wheat  breakfast  food 

Beef,  round 

Milk 

Mutton 

Pork 

Rice 

Eggs 

Beef,  sirloin 

Pork-fat,  salt 

Com,  canned 

Butter 

* 

1                1                1 

1                1                1 

1                1 

1-350  of  a  pound 

*  Each  division  in  this  scale  is  one- tenth  pound. 

Carbohydrate  Yielding  Foods. — Carbohydrate  yielding  foods 
are  almost  wholly  vegetable,  as  animal  substances  furnish 
only  a  small  amount  of  starch  or  sugar.     Milk,  containing 


FOODS  AND  FOOD  HABITS 


43 


4%  milk  sugar,  is  the  only  important  animal  source.  All 
foods  of  vegetable  origin,  especially  the  cereals,  wheat,  corn, 
oats,  etc.,  furnish  some  starch.  Peas,  beans,  and  potatoes 
all  yield  moderate  amounts  of  starch  only  (Fig.  20.)  This  is 
because  potatoes  contain  much  water,  while  peas,  beans,  etc., 
are  composed  one  third  to  one  fourth  of  proteid.  Leafy  vege- 
tables, e.g.,  cabbage,  and  lettuce,  yield  almost  no  food  proper. 

Vegetable  foods  also  contain  sugars,  though  they  are 
not  so  common  as  starches  and  hence  not  so  cheap.  Sugar 
cane  and  sugar  beet  provide  us  with  the  greatest  quantity, 
this  sort  of  sugar  being  called  saccharose.  Fruits  contain 
considerable  sugar  of  a  type  called  fruit  sugar,  glucose  or 
dextrose.  It  is  not  so  sweet  as  cane  sugar,  but  its  food  value 
is  just  as  great.  Chemists  can  easily  make  this  form  of  sugar 
from  starch,  and  can  produce  it  in  this  way  quite  cheaply. 
This  fact  has  caused  it  to  be  used  frequently  in  the  adultera- 
tion of  cane  sugar  and  very  clear,  colorless  syrups.  The 
fact  that  it  has  very  little  sweetening  power  makes  it  necessary 
to  use  more  of  it  to  produce  the  desired  sweet  taste;  it 
is,  therefore,  an  undesirable  adulterant  for  cane  or  for  beet 
sugar. 

PERCENTAGE  OF  CARBOHYDRATES  IN  COMMON  FOODS 


Sugar 
Rice 

Wheat  flour 
Corn  meal 
Oat  meal 
Peas  or  beans 
Graham  bread 
Wheat  bread 
Potatoes 
Green  corn 
Milk 

Tomatoes 
Meats 

98 
79 
75 
75 
68 
60 
54 
57 
18 
14 
5 
.2 

0 

44 


ADVANCED  PHYSIOLOGY 


Fat  Yielding  Foods. — Fats  are  present  in  both  animal  and 
vegetable  foods,  although  the  larger  amounts  come  from 
animal  sources,  and  the  most  common  fats  are  those  in  meats. 
Lard  is  a  fat  from  pork,  and  butter  is  simply  the  fat  taken 


Bi 


ii  I  iiiKiii  im[|ii  iiiiililh;  M!!;  i!'; 
■|.|;!i;j!!!!!li!!!!l!ii|i!:;i!i!ii:!:!Ci!!i 


Milk 


duHer 


Ch 


esse 


Fig.  21. — Showing  the  food  value  of  milk,  butter  and  cheese 

The  shading  as  in  Figure  19. 

from  milk,  which  is  an  animal  product;  Fig.  21.  From  vege- 
table products,  e.  g.  olives,  corn  and  nuts,  more  or  less  fat 
is  obtained,  generally  in  the  form  of  oil. 

PERCENTAGE  OF  FATS  IN  COMMON  FOODS 


Butter 
Salt  pork 
Mutton 
Beef 
Fish 


Oatmeal 
Milk 

Corn  meal 
Rice 
Beans 
Wheat  flour 
Peas 
Potatoes 


85 
60 
22 
20 

10 
8 
3.5 
2.2 
.4 
.2 
.1 
.1 
.1 


Varies  from  .2  to  20% 


II 


FOODS  ANB  FOOD  HABITS  45 

Some  Characteristics  of  Fats. — Some  fats,  e.  g.  butter, 
are  very  pleasant  to  taste,  while  others,  like  castor  oil,  are 
decidedly  unpleasant;  some  are  easily  swallowed,  while  others 
can  be  swallowed  only  with  difficulty.  The  reason  for  this 
is  that  three  different  kinds  of  fatty  materials  are  mixed 
together  in  the  ordinary  fats  of  our  foods;  one  of  these, 
called  olein,  melts  at  23°  F.  (-5°  C);  a  second,  palmatin,  melts 
at  113°  F.  (45°  C);  and  a  third,  stearin,  melts  at  140°  F. 
(60°  C.)-  It  is  easy  to  see  that  the  more  olein  a  fat  contains 
the  more  easily  it  can  be  melted.  Olive  oil  is  mostly  olein 
and  is  melted  at  ordinary  temperatures,  while  beef  tallow 
contains  much  stearin  and  is  solid  even  at  the  ordinary 
temperature  of  the  body.  Butter  and  lard  are  quite  soft 
because  they  contain  a  large  proportion  of  the  easily  melted 
olein.  It  is  well  to  remember  also,  that  the  easily  melted  fats 
are  the  most  readily  digested. 

Fats  constitute  an  extremely  important  part  of  our  food 
since  they  are  so  easily  digested  and  yield  so  much  energy. 
All  fats,  whatever  their  special  natures  or  flavors,  serve  much 
the  same  purpose. 

Vitamines. — Until  very  recently  it  has  been  believed  that 
the  three  food  materials  above  discussed,  together  with  salts 
and  water,  were  all  that  is  necessary  for  an  ample  diet,  and 
that  new  protoplasm  is  readily  made  from  them  alone.  Cer- 
tain diseases,  e.g.,  a  form  of  neuritis  (''beri-beri"),  an  intestinal 
disorder  (scurvy),  and  rickets,  were  explained  as  due  to  the 
use  of  incorrect  proportions  of  the  foods  already  mentioned. 

It  is  now  clearly  proven  that  substances  called  vitamines 
must  also  be  eaten  and  when  used,  the  illnesses  referred  to  do 
not  occur,  or  if  present,  are  cured. 

Vitamines  are  found  in  the  seed  coats  of  most  cereal  grains, 
in  yeast,  in  whole  milk  and  butter,  in  eggs,  in  leafy  vegetables 
(especially  spinach),  and  in  the  juices  of  commonly  eaten 
fruits,  e.  g.,  oranges,  apples,  etc.  These  substances  are 
destroyed  in  boiled  milk,  and  as  fruits  are  heated  when  canned. 


46  ADVANCED   PHYSIOLOGY 

such  should  not  be  considered  as  satisfactory  substitutes  for 
fresh  fruits.  Again,  in  this  connection,  the  necessity  for  a 
varied  diet  is  clearly  emphasized. 

COMPOSITION  OF  COMMON  FOODS 

Milk,  taken  alone,  is  a  complete  food,  containing  all  nec- 
essary materials.  Its  composition  is  approximately, — proteid, 
2.5%;  fat,  4%;  sugar,  5%;  water,  88%.  Milk  should  be 
considered  a  food  and  not  a  beverage;  it  contains  a  higher 
percentage  of  solids  than  any  of  the  commonly  used  vegetables 
except  peas  and  beans. 

Butter  is  the  fat  of  milk  and  little  else.  It  contains  prac- 
tically no  tissue  building  substances,  but  is  useful  to  accom- 
pany other  foods,  like  bread,  which  are  deficient  in  fat; 
Fig.  21. 

Cheese  contains  all  the  proteid  in  milk,  together  with 
most  of  its  fat.  There  is  almost  no  carbohydrate  in  it,  how- 
ever, and  while  very  nutritious  because  of  its  high  percentage 
of  proteid  (30%  or  more),  it  should  be  eaten  only  with 
other  foods  containing  sugars  or  starches,  e.  g.  bread  oj 
crackers. 

Meats  always  contain  large  amounts  of  proteid  as  well 
considerable  fat.  They  are  among  the  most  easily  digestec 
of  the  proteid  foods.  Meats  contain  no  carbohydrates  an< 
should  not  be  eaten  alone,  but  should  be  accompanied  h] 
some  starchy  foods,  such  as  bread  or  potatoes. 

Eggs  should  be  classed  with  meats  since  they  contain  aboi 
the  same  kinds  of  material,  and  should  be  used  in  the  sai 
way. 

Bread  is  one  of  the  best  foods.  It  contains  considerable" 
proteid  and  a  large  amount  of  starch.  The  fat  present  is  not 
sufficient  to  make  bread  a  balanced  food,  but  we  commonly 
eat  it  with  butter.  Bread  and  butter  alone  make  an  almost 
perfect  diet. 


FOODS  AND  FOOD  HABITS 


47 


Cereals — The  various  breakfast  cereals  are  all  excellent 
foods  and  rank  with  bread  in  food  value.  They  are  made 
mostly  of  wheat  or  oats,  both  of  which  contain  much  proteid 
and  starch;  Fig.  22.  They  are  somewhat  lacking  in  fat, 
but  if  eaten  with  cream 
form  an  almost  perfect 
food. 

Rice  contains  less  pro- 
teid than  wheat  and,  like 
it,  very  little  fat.  It 
should,  therefore,  be  eaten 
with  some  food  contain- 
ing more  proteid,  e.  g. 
meats,  cheese  or  beans.  Fig.  22.— Showing  the  food  values 

Beans  and  peas  contain         of  wheat  flour  and  oatmeal 

very  large   amounts  of  pro-  Shading  as  in  Figure  19. 

teid,  as  much  as  meats  or  even  more.  Although  they  also 
hold  considerable  starch,  they  are  to  be  looked  upon  chiefly  as  a 
source  of  proteid.  To  form  a  balanced  diet  they  should  be 
accompanied  by  some  food  containing  starch  and  fats,  such 
as  bread  and  butter.  Peas  and  beans  are  difficult  to  digest 
and  should  be  eaten  somewhat  sparingly. 

Potatoes  have  a  relatively  small  food  value.  They  contain 
only  1.8%  of  proteid,  14.7%  of  starch  and  little  fat;  Fig.  20 
They  are  very  poor  foods  if  used  alone,  and  must  be  eaten 
in  great  quantities  to  supply  the  requisite  amount  of  proteid. 
They  do,  however,  furnish  a  cheap  source  of  starch  and  are, 
therefore,  valuable  to  accompany  other  foods  such  as  meats, 
cheese,  beans  etc. 

Vegetables,  as  a  rule,  contain  so  little  real  nutriment  that 
we  can  scarcely  consider  them  foods  at  all.  They  are  valu- 
able because  of  their  pleasant  flavors,  which  stimulate  the 
action  of  the  digestive  glands. 

Fruits  furnish  about  the  same  elements  as  vegetables. 
They  have  pleasant  flavors  which  excite  proper  activity  in 


IS  ADVANCED  PHYSIOLOGY 

the  digestive  organs.  It  is,  therefore,  useful  in  regulating 
digestion,  but  does  not  furnish  much  nutriment. 

Nuts  contain  fat  and  in  some  cases  much  sugar  and  pro- 
teid;  Fig.  20.  In  spite  of  the  fact  that  they  are  used 
extensively  by  vegetarians,  they  are,  unfortunately,  hard  to 
digest. 

Confectionery  is  a  real  food  and  not  simply  a  luxury.  It 
furnishes  fuel  food  only,  but  this  in  large  amounts.  A  pound 
of  candy  will  yield  about  two-thirds  of  the  fuel  needed  by 
the  body  during  a  day. 

THE  AMOUNT  OF  FOOD  NEEDED 

Even  when  the  body  seems  to  be  perfectly  quiet  it  is  doing 
much  work.    The  heart  is  beating,  the  blood  is  circulating, 
the  chest  is  moving.    Much  heat  is  constantly  demanded  to 
maintain  internal  temperature  and  to  counterbalance   that 
given  off  from  the  surface.     The  body,  even  when  quiet  in 
sleep,  is  giving  off  heat  about  as  fast  as  a   sixteen- candle 
power  electric  lamp;   and  when  awake,  but  resting,  as  much 
as  a  twenty-candle  power  lamp.    The  total  amount  of  enerj 
expended  in  various  ways  by  the  body  may  be  better  appn 
ciated  when  it  is  noted  that  an  ordinary  person  while  remaii 
ing  quiet  for  a  whole  day  uses  up  an  amount  of  energy  eqi 
to  that  required  in   climbing   a    mountain    five    thousai 
feet  high.    This  measurement  of  energy  is  usually  express( 
in  terms  of  heat    units,  called   calories.     A  calorie*  is  tl 
amount  of  heat  required  to  raise  the  temperature  of  one  kilc 
gram  (about  one  pint)  of  water  about  two  degrees  F. ;  and  tl 
resting  body  uses  from  2000  to  2300  of  these  units  in  twent] 
four  hours.    If  a  man  rises  from  his  chair,  walks  about  eighj 
feet  and  returns,  he  uses  about  one  unit.     When  a  person  is 
working  he  liberates  more  heat  and  expends  more  energy  than 
when  quiet;  in  order  to  do  this  he  must  oxidize  more  food.    The 
working  man  may  use  two  to  four  times  as  much  food  as  one 

*This  is  the  large  calorie;  not  the  small  one,  which  is  only  y^^  as 
great;  i.e.,  the  amount  of  heat  required  to  raise  the  temperature  ©f 
<ir\e  grain  of  water  1°  C. 


I 


FOODS  AND  FOOD  HABITS  49 

resting,  and  a  fair  day's  work  would  require  an  extra  amount 
of  fuel  food  equal  to  about  one  pound  of  sugar  or  starch,  or 
I  about  one-half  pound  of  fat.  A  working  man's  diet  should 
contain  more  carbohydrates  and  fats  but  little  if  any  more 
proteid  than  that  of  a  person  of  sedentary  occupation.  A 
large  person  needs  more  food  than  a  small  one  and  an  adtdt 
more  than  a  child. 

Hence  no  fixed  amount  of  food  would  be  the  correct  one 
for  every  person.  The  amounts  of  some  common  foods  in 
either  of  the  following  rations  represent  approximately  what 
is  required  each  day  by  an  average  adult  person  doing  a  moder- 
ate amount  of  work: 

A  DAY'S  RATION 

I. — Lean  meat,  i  lb.  (a  piece  as  big  as  a  man's  hand) 
Potatoes,  1  lb. 
One  glass  of  milk 
Bread,  ^  lb.  (^  of  a  small  loaf) 
Butter,  sufficient  to  go  with  the  bread 

II.— Bread  (with  butter),  1  lb. 
Milk,  1  pt. 
Cheese,  2  oz. 
Eggs,  2 
Fruit 

If  one  eats  three  meals  a  day,  the  amounts  mentioned  in 
either  list  given  above  should,  of  course,  be  distributed  through 
the  three  meals.  The  rations  outlined  differ  slightly  in  the 
total  amount  of  food  they  contain,  but  they  are  nearly  equiv- 
alent in  nutriment.  The  amount  of  proteid  in  each  is  less 
than  some  think  necessary,  and  more  than  others  advise. 

Overeating. — Overeating  may  result  from  eating  too  much 
at  a  meal  or  from  eating  too  frequently.  Undoubtedly 
Americans  suffer  from  eating  too  much.  The  difficulty  of 
saying  just  how  much  a  person  should  eat  makes  it  equally 


60  ADVANCED  PHYSIOLOGY 

difficult  to  define  what  is  meant  by  overeating.  In  general, 
if  one  eats  till  he  feels  surfeited,  or  if  he  adds  a  dessert 
after  he  has  satisfied  his  appetite,  he  is  overeating  and  will 
probably  suffer  for  it.  A  dessert  is  frequently  a  misfortune, 
since  it  is  added  to  a  meal  to  please  the  sense  of  taste 
rather  than  to  satisfy  the  appetite.  A  growing  boy  or  girl 
needs  more  food  than  an  adult,  and  overeating,  though  a 
common  fault  with  grown  people,  is  not  likely  to  occur  with 
children. 

Frequency  of  meals. — Most  Americans  are  in  the  habit  of 
taking  three  meals  a  day  and  regard  this  as  necessary  to  health. 
In  reality  frequency  of  eating  is  simply  a  matter  of  habit. 
Some  nations  are  in  the  habit  of  taking  four  or  even  five  meals 
in  a  day,  others  eat  only  two,  while  savage  tribes  eat  very 
irregularly,  often  only  once  in  two  or  three  days,  without 
suffering  in  health.  No  rule  can  be  given  as  to  the  proper 
time  that  should  elapse  betv/een  meals.  It  is  unwise,  however, 
to  eat  too  frequently.  Breakfast,  if  eaten  immediately  afte] 
the  long  sleep,  should  ordinarily  be  the  lightest  meal  of  t 
day,  since  the  digestive  organs  are  not  ready  to  begin  work 
quickly  as  the  brain.  The  hearty  meal  should  be  preferabl; 
at  the  close  of  the  day's  work,  and  should  be  followed  by  rest  for 
an  hour  or  more.  Mental  work  immediately  after  eating  seems 
to  interfere  with  digestion  less  than  does  muscular  exercise. 
A  little  food  before  going  to  bed  may  not  be  injurious,  and  is 
frequently  advantageous  in  enabling  one  to  sleep  more  easily. 
A  hearty  meal  before  retiring  is,  however,  not  advisable. 
Among  other  bad  effects  it  is  likely  to  produce  unpleasant 
dreams. 

The  Appetite  as  a  Guide  in  Eating. — The  only  guide  which 
nature  has  given  us  as  to  the  amount  and  kind  of  food  we 
should  eat  and  the  liquid  we  should  drink  is  the  appetite. 
Lack  of  food  produces  hunger  which  is  felt  in  the  stomach, 
and  lack  of  water  produces  thirst  which  is  ipiii  in  the 
throat. 


1 


POODS  AND  FOOD  HABITS  51 

When  a  person  is  in  health  the  appetite  is  a  tolerably  safe 
guide  as  to  the  amount  he  should  eat.  This  is  true  only  pro- 
vided he  distinguishes  between  a  real  desire  for  food  and  a 
desire  to  please  the  taste,  as  for  example,  when  eating  candy. 
If  he  should  continue  to  eat  and  drink  after  his  appetite  is  ap- 
peased, he  will  do  himself  an  injury.  He  who  mistakes  the  pleas- 
ure of  gratifying  his  taste  for  that  of  satisfying  his  appetite  be- 
comes intemperate  and  is  almost  sure  to  lay  the  foundation  for 
digestive  troubles. 

Since  the  appetite  is  the  guide  that  most  people  follow 
each  person  should  be  particularly  careful  not  to  abuse 
it  by  improper  habits.  If  he  Uves  upon  good,  wholesome, 
plain  food  and  drinks  water,  he  may  rely  on  his  appetite; 
but  if  he  pampers  it  with  rich,  highly  seasoned  foods,  or 
if  he  injures  it  by  overeating  or  by  so-called  alcoholic 
stimulants,  he  cannot  depend  upon  it.  If  one  leads  a 
sedentary  Ufe,  his  appetite  is  likely  to  fail  and  he  should 
arouse  it  by  exercise  rather  than  tempt  it  with  rich,  highly 
flavored  dishes. 

VEGETARIANISM 

Some  people  believe  that  a  meat  diet  should  be  avoided 
and  that  a  vegetable  menu  is  conducive  to  better  physical 
health.  These  people  are  called  vegetarians,  although  they 
eat  freely  of  eggs  and  drink  milk.  Most  vegetables  contain  a 
very  limited  percentage  of  proteid;  some,  like  cabbage,  lettuce, 
tomatoes,  beets,  turnips,  spinach  and  fruits,  contain  practically 
no  proteids,  and  while  they  are  of  value  in  stimulating  the  di- 
gestive tract  they  do  not  furnish  much  nutriment. 

The  body  is  constantly  demanding  proteid,  and  while 
some  vegetable  foods,  such  as  potatoes  and  cereals,  contain 
large  amounts  of  starch,  they  contain  relatively  smaller 
amounts  of  proteid  than  do  meats.  Experiment,  too,  has  shown 
that  the  proteids  of  vegetables  do  not  nourish  the  body  as  well 
as  equal  amounts  of  animal  proteids.    One  could  in  time  gather 


62  ADVANCED  PHYSIOLOGY 

a  good  deal  of  wheat  by  searching  over  the  wheat  fields  and 
picking  up  the  stray  stalks  left  by  the  reapers;  but  it  would 
be  much  simpler  to  take  it  from  the  wheat  bins  where  large 
quantities  are  stored.  Likewise  enough  proteid  will  be  obtained 
if  enough  vegetable  food  is  eaten;  but  this  would  usually  in- 
volve the  consumption  of  too  much  starch.  It  is  better, 
therefore,  to  obtain  proteid  from  the  more  concentrated  foods. 
Some  of  the  cereals,  especially  wheat,  contain  large  quantities, 
as  do  beans  and  peas.  Animal  foods,  as  a  whole,  contain 
large  amounts,  which  are  more  easily  digested  and  of  more 
value  to  the  body  than  the  proteids  of  vegetable  foods. 

Against  the  use  of  meats,  on  the  other  hand,  several  objec- 
tions are  urged.  First  is  the  claim  that  the  frequent  use  of 
meat  involves  the  eating  of  too  much  proteid.  This  is  especially 
true  of  those  who  eat  in  restaurants  and  hotels,  for  with  the 
menu  of  the  restaurant  before  him  almost  every  one  will  choose 
meat.  It  is  believed  that  on-^  of  the  primary  causes  of  the 
kidney  trouble  prevalent  among  the  American  people  is  the 
excessive  amounts  of  meat  which  are  eaten  in  a  country  where 
that  kind  of  food  is  comparatively  cheap.  Further  it  is  urged 
that  by  means  of  animal  foods  certain  injurious  parasites 
such  as  tapeworms  and  trichinae  are  sometimes  introduced 
into  the  body;  all  these  disastrous  effects  would  be  avoided 
if  we  refrained  from  eating  meats. 

Whatever  one  may  think  of  the  matter,  vegetarianism  is 
certainly  a  wholesome  reaction  against  the  food  habits  of 
certain  classes  of  people  who  make  meat  the  basis  of  every 
meal.  There  is,  however,  no  good  reason  why  meat  should 
not,  in  proper  proportion,  form  a  limited  part  of  our  diet  each 
day. 

INCIDENTAL  ARTICLES  OF  FOOD  f 

Condiments. — The  spices — pepper,  cinnamon,  allspice,  muS' 
lard,  nutmeg  etc. — common  table  salt,  the  flavorings  used  in 
foods,  and  the  flavoring  part  of  syrups  used  in  drinks  are  all 


FOODS  AND  FOOD  HABITS  53 

condiments.  None  of  these  is  really  a  food,  since.it  con- 
tains no  nourishment;  but  they  are  all  useful  in  one  of  two 
ways:  as  agents  for  producing  a  .pleasanter  taste  in  some 
foods  or  as  stimulants  to  provoke  a  more  rapid  flow  of  some 
of  the  digestive  juices.  Common  table  salt  seems  to  be  a 
necessity. 

Other  Materials  Needed. — It  will  be  seen  from  the  figure  on 
page  26  that  besides  the  constituents  of  the  three  chief  food 
substances  the  body  contains  a  small  but  appreciable  amount 
of  other  materials.  Compounds  of  iron,  sulfur,  potassium 
and  other  elements,  are  all  present  in  small  amounts.  One 
of  these,  the  necessity  of  which  is  easily  appreciated,  is  the 
mineral  matter  that  forms  the  hard,  resisting  part  of  bones — 
calcium  phosphate,  or  phosphate  of  lime,  as  it  is  sometimes 
called.  Although  one  does  not  realize  that  he  is  consuming 
lime  in  his  food,  many  foods  contain  it.  It  is  present  in  eggs, 
as  is  shown  by  the  fact  that  a  chicken  has  bones  when  it  is 
hatched.  It  is  in  wheat,  also,  and  in  meats  in  small  amounts. 
In  short,  our  common  foods  contain  enough  of  this  material 
to  supply  all  the  lime  we  need  for  bone  formation  and 
repair. 

Sometimes  a  child  whose  bones  are  growing  rapidly  may 
eat  so  much  sugar-containing  food,  such  as  cake,  pastry  and 
candy,  that  he  gets  too  little  of  the  more  substantial  foods 
and  fails  to  obtain  the  proper  material  for  his  bones  and  teeth. 
This  is  occasionally  shown  by  the  rapid  decay  of  the  teeth 
and  in  permanently  crooked  bones  in  the  legs,  a  condition 
called  rickets.  A  more  substantial  diet  of  bread,  eggs  and  meat 
would  be  advisable  in  such  cases. 

COOKING 

Everyone  should  know  something  about  cooking.  Cooking 
always  means  the  appHcation  of  heat  in  some  form  to  a  raw 
food.  Sometimes  it  is  done  by  placing  the  food  in  dry,  hot 
air — baking  or  roasting;    sometimes  by  putting  the  food  in 


54 


ADVANCED  PHYSIOLOGY 


Fig.    23. — The  cells  of  a  potato 

Showing  the  inclosed  starch  grains. 


boiling  water — boiling;    sometimes  by  submerging  the  ma- 
terial in  hot  or  melted  i&t— frying.     Heat  has  a  variety  of 

effects  upon  food  and  pro- 
duces some  decided  chemical 
changes. 

Few  foods  except  milk  and 
fruit  are  palatable  in  their 
natural  state.  Cooking  food 
improves  it  in  three  differ- 
ent ways:  (1)  in  flavor,  (2)  in 
digestibility,  (3)  in  safety  as 
food. 

1.  The  change  in  flavor  is 
very  great,  so  great  indeed, 
that  in  some  cases  our  taste 
hardly  recognizes  the  raw  and 
the  cooked  food  as  being  the  same  material.  The  '^culj 
tivated"  tastes  of  the  present  day  make  people  fastidioi 
as  to  the  flavors  of  foods.  They  seldom  stop  to  question 
the  nutritive  value   of    a    particular    dish,    but    select    foo( 

with   reference  to  their  flavoi 
eating  those  that  are  palatabl 
whether  they  are  nutritious 
not.      An    agreeable    flavor 
important,    since   it   enables 
more  easily  to  digest  our  foo< 

2.  Exposure  to  heat  and 
the  hot  fluids  in  which  foo( 
are  cooked  does  much  towarc 
softening  food,  ''making  it  tenj 
der,"  so  that  later  it  readil] 
falls  to  pieces  under  the  actioi 
of  digestive  ferments  and  the  mechanical  grinding  of  th^ 
mouth  and  stomach.  Vegetable  foods,  especially,  nee^ 
cooking.    The  walls  of  the  plant  cells  resist  digestive  ageni 


Fig.  24. —  Showing  how  cooking 
bursts    the    starch-holding 

CELLS 


FOODS  AND  FOOD  HABITS 


55 


hut  the  heat  of  cooking  breaks  them,  setting  free  the  starch 
granules  which  swell  and  burst  under  the  influence  of  heat 
and  are  thus  more  thoroughly  and  easily  acted  upon  by  the 
saliva  and  other  digestive  juices;  Figs.  23  and  24.  Heat 
acts  upon  starch  much  as  it  does  upon  grains  of  corn.  We 
can  easily  see  that  popped  corn  must  be  more  readily  digested 

,  than  unpopped  kernels.     So  far  as  ease 

I  of  digestion  is  concerned  the  cooking 
of  animal  foods  is  not  so  important, 
since  the  connective  tissue  which  holds 
the  muscle  fibres  together  is  easily  dis- 
solved by  the  digestive  juices.  Indeed, 
most  meats  are  more  easily  digested 
uncooked,  since  the  proteid  in  them 
is  coagulated  by  heat,  and  must  be 
turned  back  again  to  a  liquid  condition 
before  it  can  be  absorbed.  Frying,  dur- 
ing which  process  the  food  becomes 
coated  with  fat,  makes  digestion  diffi- 
cult. 

3.  There  is  another  entirely  sufficient 
reason  for  extreme  care  in  the  cooking 
of  meats;  this  is  the  liability  that  para- 
sites of  some  kind  may  be  present  in  the 
meat  fibres.  Such  parasites  are  found 
more  commonly  in  pork  than  in  any 
other  kind  of  meat  generally  eaten.  An 
apparently  excellent  piece  of  pork  may 
contain  in  a  single  ounce  as  many  as  85,000  of  these  little, 
round  worms,  trichinae;  Fig.  25.  If  these  are  swallowed 
without  being  killed  by  thorough  cooking,  they  wander  out 
through  the  walls  of  the  human  food  canal  and  take  up 
their  abode  in  the  voluntary  muscles  of  the  body.  As  each 
female  trichina  may  produce  a  thousand  or  more  young,  it 
10  evident  that  a  serious  disease,  trichinosis,  may  result. 


A 

Fig.    25. —  A,    single 

TRICHINA.    B,  A  BIT  OP 
MUSCLE  OF    PORK 
Showing   trichina  between 
the  fibres 


66  ADVANCED  PHYSIOLOGY 

The  young  of  the  tapeworm  also  may  be  concealed  in  meats, 
ready  to  attach  themselves  to  the  wall  of  the  intestine  as 
soon  as  liberated  from  the  meat  by  the  digestive  juices. 
This  animal  never  afterwards  leaves  the  digestive  tract,  and  its 
presence  there  is  by  no  means  fatal,  although  it  sometimes 
attains  great  size  and  absorbs  much  of  the  nutrition  which 
should  go  to  feed  its  human  host. 

The  practice  of  wholly  or  partially  cooking  milk  is  becoming 
more  and  more  common.  These  processes  are  called  steri- 
lizing and  pasteurizing.  When  milk  is  sterilized,  it  is  heated 
at  least  to  the  temperature  of  boiling  water,  212°  F.;  when 
it  is  pasteurized,  it  is  not  heated  so  much,  usually  to  about 
165°  F.  In  either  case  the  purpose  is  to  destroy  the  micro- 
scopic germs  which  it  contains.  Milk,  since  it  is  such  a  nutri- 
tious food,  furnishes  an  excellent  abode  for  numerous  bac- 
teria. It  is  not  uncommon  to  find  100,000  bacteria  in  a  single 
drop  of  city  milk.  Most  of  these  are  quite  harmless  and  may 
exist  in  the  milk  in  great  numbers  without  particularly 
injuring  it.  But  sometimes,  unfortunately,  germs  of  serious 
diseases  find  their  way  into  milk.  Bacteria  of  typhoid  fever, 
tuberculosis,  scarlet  fever  and  diphtheria  are  sometimes  thus 
distributed.  The  germs  that  produce  these  diseases  may 
easily  be  killed  by  heat,  even  by  the  moderate  heat  of  165° 
if  it  be  rightly  applied,  and  thus  the  milk  may  be  rendered 


Water. — "Do  you  drink  plenty  of  water  every  day?"  is 
a  question  which  a  good  physician  often  asks  his  patients; 
and  in  giving  medicine  he  may  prescribe  a  whole  glass  of 
water  with  a  very  small  pill.  It  has  been  stated  that  three- 
quarters  of  the  "blues,"  ''gray  days"  and  "east  winds" 
which  come  over  people,  discouraging  and  depressing  them, 
would  be  escaped  if  they  would  only  drink  a  sufficient  amount 
of  cold  water. 

All  living  matter,  i.e.  all  protoplasm,  contains  water;  and 
while  we  cannot  say  that  water  is  a  food,  we  do  know  that  it 


FOODS  AND  FOOD  HABITS  57 

is  vitally  necessary  to  us.  No  solid  matter  can  be  absorbed 
into  the  blood;  everything  must  be  dissolved  and  reduced  to 
a  thin  liquid  in  order  to  pass  through  the  walls  of  the  intes- 
tine. The  water  necessary  for  this  must  be  present,  or  ab- 
sorption cannot  take  place. 

If  the  food  in  the  intestine  is  in  a  comparatively  dry  con- 
dition, it  is  moved  along  with  difficulty,  and  indigestion  may 
be  the  result.  We  are  more  likely  to  drink  water  too  cold  than 
to  drink  it  in  too  great  quantities;  if  very  cold,  it  may  chill 
the  secreting  surfaces,  thus  retarding  their  work  and  inter- 
fering with  digestion.  The  amount  of  water  given  off  through 
the  lungs  is  about  one  pint  per  day,  from  the  skin  two  pints, 
and  through  the  kidneys,  in  the  case  of  an  average  person,  a 
little  over  three  pints  per  day.  Thus  the  demand  for  fresh 
water  is  constant. 

As  a  result  of  the  life  processes,  broken  down  products  of 
body  metabolism  are  continually  produced.  This  material 
must  be  eliminated,  and  for  this  purpose  it  must  be  dissolved 
in  the  blood  so  as  to  be  carried  to  the  excreting  organs.  If 
one  drinks  too  little  water,  the  blood  may  become  overcharged 
with  such  waste  products,  some  of  which  are  poisonous.  These 
substances,  when  too  abundant  in  the  blood,  may  dull  the 
nerve  centers,  giving  one  a  disheartened  feeling,  and  leaving 
him  in  poor  mental  condition  for  meeting  the  demands  of  life. 
By  drinking  plenty  of  water  the  body  is  kept  constantly 
"flushed,"  as  it  were,  and  one's  whole  life  is  more  vigor- 
ous and  active.  The  Japanese  soldiers  have  taught  the 
world  a  lesson  in  methods  of  preserving  health,  and 
among  other  things  have  shown  the  beneficial  results 
arising  from  drinking  large  quantities  of  pure  water  without 
''stimulants."" 

There  is  no  good  reason  why  we  should  not  drink  water 
freely  during  meals.  The  reason  sometimes  given  for  the 
contrary  view — that  water  dilutes  the  saliva  and  gastric 
juice— has  no  great  weight.    Not  only  is  water  readily  ab- 


58 


ADVANCED  PHYSIOLOGY 


sorbed,  but  digestion  proceeds  more  rapidly  when  the  Juices 
are  somewhat  diluted. 

Other  Beverages. — In  America,  the  most  commonly  used 
beverages,  other  than  water,  are  probably  coffee,  tea,  cocoa 
and  chocolate.  Cocoa  and  chocolate  are  foods,  since  they 
contain  some  fatty  material.  Coffee  and  tea,  on  the  other 
hand,  can  be  considered  only  as  stimulants.  The  active  ele- 
ment in  coffee  is  a  substance  called  caffein;  that  in  tea  is 
called  thein,  the  two  being  practically  identical.  The  degree 
to  which  these  affect  different  individuals  is  variable.  As  a 
rule  they  excite  the  nerve  centers  to  greater  activity.  This  may 
be  of  advantage  in  rare  cases;  but  not  when  one  is  in  bed, 
trying  to  sleep.  After  the  use  of  these  drinks  becomes  a 
habit,  the  nerve  centers  refuse  to  act  well  unless  urged  on 
by  this  "whip"  and  it  is  better  to  live  in  the  strength  of  one's, 
own  natural  vigor. 

The  "soft  drinks"  sold  at  soda  fountains  are  made  of  water' 
into  which  carbon  dioxid  gas  has  been  pressed.     Flavors  in 
the  form  of  syrups  are  added.     Since  carbon  dioxid  is  reallyj 
one  of  the  waste  products  of  the  body,  we  might  suppose  that 
in  our  drink  it  would  be  harmful;  but  it  is  of  real  injury  only 
when  we  breathe  it.     However,  such  drinks  are  no  better 
than  water;  they  are  expensive  and  the  syrups  may  impair 
digestion.     Lemonade  is  used  solely  for  its  agreeable  taste, 
although  the  sugar  which  is  usually  in  it  serves  to  a  small 
degree  as  food.     Some  beverages  are  advertised  as  especially  ^ 
''good  for  the  nerves,"  but  this  claim  is  largely  a  pretense 
used  for  the  purpose  of  catching  trade.     If  one  finds  any! 
drink  especially  exhilarating,  he  is  warranted  in  suspecting] 
that  it  contains  alcohol  or  a  similar  ingredient  that  produces 
temporary  excitement. 

Alcohol. — Alcohol  must  be  considered  here  because  it  has 
so  often  been  classed  as  a  food,  and  has  even  been  given  the 
unfortunate  misnomer,  "liquid  bread".  Alcohol  is  derived 
from  sugars  by  a  process  of  fermentation.     A  large  number 


FOODS  AND  FOOD  HABITS  «> 

of  vegetable  products  contain  considerable  starch  which  can 
easily  be  converted  into  sugar,  and  almost  any  of  these  may 
serve  as  a  source  of  alcohol.  The  fermenting  agent  in  all 
cases  is  yeast.  This  is  sometimes  intentionally  added  to  the 
fermentable  mass;  but  sometimes  fermentation  is  caused 
simply  by  the  action  of  the  so-called  wild  yeasts,  i.  e.  germs 
which  exist  everywhere  in  nature,  and  which  may  get  into  the 
material  from  the  air,  or  more  often  from  the  skin  of  the  fruit 
or  other  substance  which  furnishes  the  sugar.  In  wine  and 
cider  making,  for  instance,  the  yeasts  are  on  the  skius  of  the 
fruits,  having  dropped  there  from  the  air.  The  yeasts  ferment 
the  sugars,  converting  them  into  alcohol  and  carbon  dioxid, 
and  the  fermented  product  is  used  to  form  the  basis  of 
alcoholic  and  fermented  liquors. 

Alcohol  has  a  variety  of  undesirable  effects  upon  the 
different  functions  of  the  body,  and  they  are  sometimes  even 
disastrous,  as  will  be  pointed  out  from  time  to  time  in  later 
pages.  Here  a  word  is  in  place  concerning  its  possible  food 
value. 

Alcohol  has  no  power  to  build  up  the  body.  It  furnishes 
no  tissue-building  material  and  neither  makes  nor  repairs  any 
organ.  Hence  it  does  not  nourish  in  the  sense  of  building  up 
the  body.  When  taken  in  any  except  the  smallest  quantities, 
it  is  nearly  all  excreted  from  the  body  as  alcohol;  it  is  thus 
not  utilized  by  the  body  and  simply  taxes  the  excreting 
organs. 

A  small  amount  of  the  alcohol  taken,  however,  is  not  thus 
excreted  but  is  consumed  in  the  body,  and  the  effect  of  this 
small  portion  must  be  considered.  It  is  oxidized,  and  when 
alcohol  is  oxidized,  it  yields  heat.  This  will  occur  if  the  oxi- 
dation takes  place  in  a  lamp  and  none  the  less  surely  if  in  the 
body;  hence  to  a  certain  extent,  alcohol  is  a  source  of  heat. 
But  only  a  small  amount  of  our  body  heat  can  be  derived  from 
alcohol,  not  enough  to  constitute  any  considerable  part  of  the 
supply  needed  for  a  day.    Though  a  small  quantity  may  fur- 


60  ADVANCED  PHYSIOLOGY 

nish  a  little  heat,  a  larger  amount  of  alcohol  does  not  furnish 
more  heat;  it  simply  exerts  a  stronger  and  more  clearly  poison- 
ous action.  Moreover,  the  heat  is  not  really  utilized  so  effi- 
ciently as  is  the  heat  that  comes  from  the  oxidation  of  sugars; 
for  one  of  the  first  effects  of  alcohol  on  the  body  is  to  enlarge  the 
blood  vessels  in  the  skin,  producing  a  flushed  condition.  This 
at  once  causes  an  increased  loss  of  heat  and  in  many  cases, 
if  not  in  all,  more  heat  is  lost  in  this  way  than  is  gained  from 
the  alcohol  oxidized.  The  total  result  is,  therefore,  a  loss  rather 
than  a  gain  of  heat. 

When  we  consider  its  further  effects  on  the  body,  we  soon 
find  that  it  cannot  properly  be  classed  with  the  fuel  foods 
like  starch  and  sugar.  Gunpowder  if  placed  in  a  stove  will 
yield  plenty  of  heat,  but  notwithstanding  this  fact,  it  should 
certainly  not  be  classed  with  fuels  like  wood  and  coal.  So 
alcohol,  even  though  it  yields  heat,  has  at  the  same  time  such 
undesirable  effects  upon  the  body  as  to  destroy  its  value 
as  a  fuel  food.  The  most  exhaustive  study  has  shown  that 
alcohol  is  certainly  a  poison,  interfering  with  the  normal 
action  of  the  cells  of  the  body,  and  above  all,  with  the  nor- 
mal action  of  the  brain.  This  will  be  considered  at  length  in 
a  later  chapter. 

Nor  is  there  any  difference  of  opinion  as  to  the  wisest 
course  to  pursue  in  regard  to  the  use  of  all  forms  of  alcoholic 
drinks.  They  are  all  injurious,  tending  to  throw  the  organs 
out  of  order,  especially  those  ot  the  nervous  system,  and  they 
interfere  with  a  healthful  vigoroup  life.  Everyone  who 
indulges  in  them  at  all  is  occasionally  or  constantly  under  the 
influence  of  their  poisoning  effect,  and  the  onlr  safe  course 
is  to  avoid  their  use  entirely. 

Concerning  these  facts  there  is  no  question-  The  dispuce 
as  to  whether  alcohol  should  or  should  not  be  called  a  fooa 
has  been  due  to  a  difference  in  opinion  as  to  the  definition 
of  the  word  food  and  need  not  concern  us.  The  accepted 
^^cts  are  clear  and  definite:     alcohol  is  primarily  a  cellular 


^^OODS  AND  FOOD  HABITS  61 

and  nerve  poison.  If  used  in  very  small  quantities  it  may 
yield  heat  and  energy  but  whatever  value  it  might  have  in 
this  respect  is  usually  quite  nullified  by  its  poisoning  action. 
For  this  reason  it  cannot  be  classed  with  fatty  and  carbo- 
hydrate foods,  and  still  less  with  proteid  foods.  The  state- 
ment sometimes  made  that  it  is  ''liquid  bread  "  is  absolutely 
false  and  misleading. 


CHAPTER  IV 


FERMENTATION  AND  GERM  DISEASES 


Before  food  can  be  absorbed  in  the  body  it  must  be  digested. 
We  shall  study  the  details  of  digestion  later,  but  before  taking 
them  up,  we  must  learn  a  little  about  the  general  process. 

The  changes  in  food  during  diges- 
tion belong  to  a  type  of  activities 
known  as  fermentation.  It  is  dif- 
ficult to  define  the  word  fermen- 
tation, and  we  can  best  learn  its 
meaning  through  illustrations. 

TYPES  OF  FERMENTATION 

Alcoholic  Fermentation. — If  to  a 

solution  of  sugar  a  little  yeast  is 
added,  an  active  change  soon  be- 
gins. The  sugar  disintegrates  and 
turns  into  alcohol  and  carbon 
dioxid  gas.  The  sugar  does  not 
change  spontaneously  but  only 
after  the  yeast  is  added,  and  the 
process  continues  until  the  sugar  is  used  up.  The  micro- 
scope shows  yeast  to  be  a  minute  living  plant;  Fig.  27. 
While  the  sugar  is  fermenting, 
the  yeast  grows  and  multiplies, 
fermentation  being  a  result  of 
its  growth.  If  the  yeast  is 
boiled,  it  is  killed  and  can 
no  longer  excite  fermentation. 
Since  this  yeast  is  a  Hving  plant     Fig.  27.— Growing  yeast  plants 

..  1         •!_  n    J  Showing  the  method  of  formation  of 

it   can   properly    be   called    an        buds  on  the  sides  of  the  ceils. 

62 


L'\n\e\JiicxVtT 

flG.      26. A      FERMENTING 

SOLUTION 

Showing  the  method  of  con- 
ducting carbon  dioxid  gas  into 
lime  water. 


FERMENTATION   AND   GERM   DISEASES  63 

organism,  and  we  speak  of  this  kind  of  fermentation  as  due 
to  an  organized  ferment. 

Later  in  this  chapter,  another  group  of  organisms,  the  bac- 
teria, are  discussed  and  their  intense  fermentative  powers  are 
pointed  out.  Being  organisms,  they  too  would  be  termed 
organized  ferments.  While  this  designation  is  a  convenient 
one  in  some  ways,  there  is  valid  objection  to  its  use.  It  is  not 
the  organisms  themselves  which  are  the  ferments,  but  rather 
the  substances  which  they  produce.  But  usage  has,  as  a 
rule,  been  that  which  is  adopted  in  this  text. 

Fermentation  of  Starch. — The  change  of  starch  to  sugar 
is  a  very  simple  one  and  is  due  to  the  union  of  starch  with  a 
little  water,  as  follows: 

C6H10O5  +  H2O  =  C6Hl20« 
Starch         Water       Sugar 

If  we  mix  starch  with  water  alone,  we  get  no  such  result; 
but  when  we  mix  starch  and  water  with  saliva,  the  combina- 
tion of  starch  with  water  begins,  and  sugar  is  formed.  This 
may  continue  until  the  starch  is  all  converted  into  sugar. 
If  we  boil  the  saliva  it  entirely  loses  this  power;  yet,  if  we^ 
study  saliva  with  a  microscope  we  find  no  living  bodies  in  it 
corresponding  to  the  yeast  plant.  Nevertheless,  there  is  some- 
thing in  the  saliva  that  provokes  this  change.  That  something 
can  be  separated  from  the  saliva,  and  when  so  separated  it 
appears  as  a  white,  structureless  powder.  It  does  not  grow, 
multiply  or  increase  like  yeast  during  the  fermentation  pro- 
cesses. Since  it  is  not  alive  it  cannot  be  called  an  organism, 
and  we  speak  of  it  as  an  unorganized  ferment;  it  is  more 
commonly  called  an  enzyme.  It  is  clearly  a  ferment  but  quite 
different  from  the  yeast  ferment.  Moreover,  when  this  enzyme 
converts  starch  into  sugar,  the  starch  and  some  water  arc 
used  up,  but  the  enzyme  remains  unaltered. 


64  •  ADVANCED  PHYSIOLOGY 

Further  than  this,  we  should  note  that  a  substance  which 
has  undergone  one  fermentative  process  and  been  broken  up 
chemically  into  two  or  more  different  substances,  may  be  still 
further  subjected  to  changes  by  other  ferments.  As  an  illus- 
tration: starch  changes  into  sugar;  sugar  may  be  broken  by 
fermentation  into  alcohol  and  carbon  dioxid;  alcohol  by 
fermentation  will  yield  acetic  acid  (the  acid  of  vinegar)  and 
water;  acetic  acid  by  fermentation  is  resolved  into  carbon 
dioxid  and  water. 

It  is  noticeable  that  the  change  is  always  from  what  is  com- 
plex to  things  which  are  simpler;  fermentation  never  produces 
the  opposite  result,  i.  e.,  is  never  constructive.  In  other 
words,  to  use  a  chemical  term,  ferments  are  catalytic  agents. 

These  two  examples  are  illustrations  of  different  types 
of  fermentation,  one  produced  by  the  growth  of  living,  micro- 
scopic plants;  the  other  by  non-living  enzymes. 

While  these  fermenting  agents  are  unlike  in  many  respects, 
their  activities  agree  in  the  following  points,  which  are,  there- 
fore, characteristic  of  fermentations.  1.  They  are  progres- 
sive chemical  changes  which  take  place  in  organic  bodies.  By 
^'progressive"  is  meant  that  when  once  begun  they  continue 
until  the  fermenting  body  is  used  up  or  until  something  stops  \ 
the  action.  2.  They  never  take  place  spontaneously,  but 
are  brought  about  by  the  addition  to  the  fermentable  body 
of  substances  called  ferments.  3.  They  are  stopped  by  the 
influence  of  heat,  and  by  the  presence  of  some  chemicals. 
4.  The  substance  which  starts  fermentation  does  not  appear ' 
to  be  used  up  in  the  process. 

When  a  substance  ferments,  its  nature  is  totally  changed; 
alcohol  and  carbon  dioxid  are  quite  different  from  sugar, 
and  sugar  is  unlike  starch.  Fermentation  always  forms  new 
substances,  and  these  new  substances  are  sometimes  good  and 
sometimes  bad  in  their  effects.  Fermentations  may  produce 
poisons  from  perfectly  harmless  substances.  When  starch 
is  turned  into  sugar,  the  product  is  a  useful  food,  but  when 
sugar  is  turned  into  alcohol,   the  product  is  dangerous  and 


FERMENTATION  AND    GERM    DISEASES  65 

extremely  harmful.  When  substances  like  meats  are  fer- 
mented (or  putrefied)  deadly  poisons  are  sometimes  pro- 
duced. Hence,  materials  that  were  originally  wholesome  and 
harmless  may,  through  fermentation,  become  unwholesome 
or  even  poisonous. 

In  the  study  of  physiology  we  are  concerned  with  both 
the  organized  and  the  unorganized  types  of  ferments,  but  in 
consideration  of  digestion  we  have  to  do  especially  with  the 
latter,  or  enzyme  type.  Several  enzymes  are  formed  in  the 
body.  Saliva  contains  one,  which  is  called  ptyalin.  The  gas- 
tric juice  contains  a  second,  called  pepsin  and  another,  called 
rennet.  The  pancreatic  fluid  probably  contains  three, — 
trypsin,  amylopsin  and  steapsin,  all  of  which  contribute  to 
the  digestion  of  food.  They  are  all  normal  products  and  are 
secreted  by  glands. 

Organized  ferments  are  living  organisms,  capable  of  growth 
and  multiplication.  Because  of  their  microscopic  size  they 
are  frequently  called  microbes;  they  are  also  called  germs; 
but  neither  of  these  terms  is  very  satisfactory,  and  it  is  better 
to  call  them  by  their  proper  name's,  yeasts  and  bacteria. 

Living  ferments,  save  when  taken  in  large  numbers,  are 
invisible  to  the  naked  eye  but  are  easily  seen  with  a  microscope. 

They    differ    from     each       ^^^^^        -v/^-^ 

other    chiefly     in     their     Q  Q    QJ  QQ 
method     of     multiplica- 
tion.      Yeasts    multiply 
by     the     formation     of 
a     small     bud     on    the  c        i — Z) 

side    of    the   plant;     Fig.      Fig.    28.— Showing    the    method    op 

07  Tk^     U-^A     «.„^^.o      ;^  MULTIPLICATION      OF      BACTERIA,       BY 

Z7,      ine   bud  grows   in  ' 

.,        _         ,f  .  .  SIMPLY   ELONGATING   AND  THEN   DIVID- 

size    until    finally    it    is         ^^^ 
as  large   as  the    original 

plant,  when  it  may  break  away  as  a  separate  one.  Bac- 
teria, however,  simply  increase  a  little  in  length  and  then 
break  in  two  in   the   middle;   Fig.   28.   Both  bacteria   and 


66 


ADVANCED  PHYSIOLOGY 


yeasts   bear    very    important    relations    to    human    health 
and  happiness. 

YEASTS 

Yeasts  are  abundant  everywhere;  they  float  in  the  air,  are 
found  in  water  and  are  in  and  on  the  ground.     Such  yeasts 

are  sometimes  called  wild 
yeasts.  Scientists  have  learned 
to  cultivate  them  in  labora- 
tories, and  they  may  be 
grown  in  great  masses.  A  cake 
of  compressed  yeast  is  simply 
a  cake  of  millions  of  these 
tiny  plants,  all  alive  and  ready 


Fig.  29 — Recently  mixed  dough, 
inoculated  with  yeast,  but 
before  the  yeast  has  grown 

(Conn,  Bacteria,  Yeasts  and  Molds). 

to  grow  if  given  proper  food. 
These  are  called  cultivated 
yeasts;  but  in  reality  the  culti- 
vated yeasts  and  the  wild  yeasts 
are  the  same  kind  of  plants. 
When  a  cook  wishes  the 
dough  "  to  rise,"  she  puts  a 
yeast  cake  in  it,  and  the  yeast, 
growing  in  the  dough,  ferments  sugar  in  the  starch  of  the 
fiour,    producing    bubbles    of   gas,    which  make  the  cUugh 


Fig.     30. — The     same     dough 

AFTER  yeast  HAS  GROWN  AND 
CAUSED  THE  DOUGH  TO  SWELL 
BY  THE  ACCUMULATION  OF  GAS 
(Conn,  Bacteria,  Yeasts  and  Molds), 


FERMENTATION   AND   GERM   DISEASES  67 

''swell";  Figs  29  and  30.  Alcohol  also  is  produced,  but  passes 
off  when  the  bread  is  baked.  The  use  of  baking  soda  in  pre- 
paring food  materials  produces  a  lightness  due  to  bubbles 
also;  but  only  the  water  in  the  mass  is  affected  by  its  presence. 
When  a  brewer  makes  beer,  he  makes  a  solution  from  certain 
grains,  containing  starch  which  is  changed  into  sugar,  and 
l^lants  yeast  in  it.  The  yeast  grows  and  destroys  the  sugar, 
producing  alcohol  and  carbonic  acid  gas.  In  the  making  of 
cider  or  wine,  when  the  sweet  juice  from  apples  or  grapes  is 
squeezed  out  and  placed  in  barrels,  the  wild  yeasts  from  the 
air  grow  in  it,  producing  the  same  changes. 

BACTERIA 

Bacteria  are  more  abundant  than  yeasts  and  are  even 
smaller  (Fig.  31);  they  are  so  small  that  sometimes  50,00lr 
of  them,  side  by  side, 
would  reach  only  an  inch. 
But  small  as  they  are, 
they  play  a  very  impor- 
tant part  in  our  lives  and 
in  the  world.  It  may  seem 
strange  that  organisms  as  Fig.  31.— Showing  the  comparative 
minute  as  these  can  have  ^^"^^  ^^  '^^^  ^^™^  ^^  ^^^  ^^^^^'^ 

.     -   ,  „       ^  .  CAMBRIC  NEEDLE   (a),  A  PARTICLE     OF 

an  appreciable  effect.     A  bust  (6),  bacteria  (c),  and  yeasts  (d) 

single    one,    to    be   sure, 

could  do  very  little;  but  bacteria  have  such  wonderful  powers 
of  reproduction  that  they  can  accomplish  much.  So  fast 
do  they  multiply  that,  under  favorable  conditions,  in  twenty- 
four  hours  a  single  one  may  have  seventeen  million  offspring, 
and  in  another  twenty-four  hours  each  of  the  first  seventeen 
millions  may  have  seventeen  million  more.  Most  people 
think  of  bacteria,  germs  or  microbes  as  our  deadly  foes.  While 
this  is  partly  true,  it  is  likewise  true  that  they  are  our  friends. 
Their  distribution  in  the  world  shows  clearly  enough  that  they 


68 


ADVANCED  PHYSIOLOGY 


Fig.    32. — A   bit  of   decaying   meat 

Highly    magnified,  showing  the  bacteria  that 
cause  its  decay. 


cannot  always  be  mischievous.     They  are  found  in  the  soil 

under  our  feet,  in  the  air  we  breathe,  in  the  water  and  milkj 

we  drink,  in  much  of  the 
food  we  eat;  Fig.  32.  They 
are  on  our  clothing,  on  our 
skin,  in  our  mouths  and 
stomachs  (Fig.  33) ;  there 
are  countless  millions  in 
the  intestine  of  every 
healthy  person. 

Beneficial    Bacteria.  — 
Although     bacteria     are 
very  small  and  are  very_ 
simple    organisms,    then 
are  many  different  kinds 
known;    and  while  some 
are   injurious,  the   great 
majority     are     harmless 

and  some  are  even  beneficiaL    One  of  the  ways  in  which 

tiiey  are  of  value  to  us  is  through  their  power  of  causing 

all  sorts  of  putrefaction  and  decay. 

This  may  not  seem  to  be  either 

useful  or  desirable.   Putrefying  and 

decaying  material  is   disagreeable 

and  its  odor   is    unpleasant,    but 

the  process  is  really  one  of  great 

value,  for  it  is  nature's  way  of  de- 
stroying the  dead  bodies  of  animals 

and  plants,  which  would  otherwise 

accumulate,   covering  the   ground 

and     fining    the    streams.       The 

bacteria   of   the   air,    ground  and 

water  attack  and  consume  all  such 

materials.    As  they  consume  them 

they  produce  gases  which  give  the  unpleasant  odors  to  the 


Fig.  33. — Bacteria  from  a 
healthy  mouth,  magni- 
FIED 


Bacteria 


THE  MICROSCOPE 
Showing  fat  drops  and  bacteria. 


FERMENTATION  AND  GERM  DISEASES  69 

decaying  bodies.  Nearly  all  kinds  of  decay  are  thus  produced 
by  bacteria  or  closely  allied  organisms.  The  putrefaction  of 
meats  and  eggs,  the  souring  of  bread  and  milk,  and  hosts  of 
other  processes  by  which 
fooa  is  spoiled  are  instances 
of  bacterial  action;   Fig.  34. 

Since  the  spoiling  of  food  is 
produced  by  bacteria,  it  fol- 
lows that  the  preservation  of 
food  for  an  indefinite  length 
of  time  is  possible  if  bacteria 
can  be  kept  from  it.  This 
is  not  an  easy  matter,  how-  Fig.  34.— A  drop  of  milk  under 
ever,  because  of  the  wide 
distribution  of  these  plants. 
They  are  sure  to  get  into  the  foods  in  spite  of  all 
ordinary  caution.  But  many  foods  may  be  protected 
from  them  by  the  process  of  canning.  In  canning,  foods 
are  first  subjected  to  a  heat  (commonly  boiling)  sufficient 
to  kill  any  bacteria  in  them,  and  then  are  sealed  up  in  jars 
or  cans  so  tightly  that  no  air  or  bacteria  can  reach  them. 
If  this  is  done  thoroughly  and  carefully,  the  food  will  keep 
indefinitely.  At  any  time  afterward  the  cans  may  be  opened 
with  the  certainty  that  the  food  will  be  found  in  good  condi- 
tion. The  discovery  of  the  methods  of  canning  has  been  of 
extreme  value,  for  it  made  it  possible  to  preserve  for  winter 
use  vast  quantities  of  food  grown  in  the  summer,  which  would 
otherwise  spoil  before  they  could  be  consumed. 

When  such  materials  are  decomposed  by  bacteria  the  prod- 
i       ucts  that  come  from  them  pass  into  the  soil  and  air  in  a  form 

I  which  can  be  used  by  subsequent  generations  of  plants.  In 
this  way  soil  is  kept  fertile,  and  we  can  depend  upon  getting, 
rear  after  year,  abundant  harvests.  Were  it  not  for  the 
Iction  of  bacteria  the  soil  would  soon  cease  to  yield  crops, 
knd  we  should  eventually  starve. 
I 


76  ABVANCED  PHYSIOLOGY 

The  flavors  of  butter  and,  in  part,  of  cheese  are  due  to  bac- 
teria. Butter  makers  have  learned  that  they  can  make 
better  butter  if  they  put  bacteria  into  the  cream  out  of  which 
butter  is  to  be  made.  They  plant  bacteria  in  cream,  much  as 
cooks  plant  yeast  in  bread  for  bread  raising,  or  farmers 
plant  grass  in  the  fields.  We  must,  therefore,  look  on  bacteria 
in  many  cases  as  our  best  friends.  When  we  remember  that 
we  have  always  carried  millions  of  them  in  our  mouths,  and 
still  have  enjoyed  good  health,  we  must  not  be  alarmed  if 
we  are  told  that  there  are  bacteria  in  water,  or  milk,  or  in  the 
air  we  breathe. 

Harmful  Bacteria. — Unfortunately  some  kinds  of  harmful 
bacteria  live  and  grow  in  the  \arious  organs  of  our  bodies. 
It  is  easy  to  understand  that  when  these  minute  parasites 
are  growing  in  great  numbers  in  different  parts  of  the  body, 
they  may  produce  trouble.  Such  troubles  are  called  diseases, 
and  to  the  bacteria  which  cause  them  is  given  the  name  of 
disease  germs,  or  pathogenic  bacteria. 

Not  all  kinds  of  disease  are  produced  by  bacteria.  Some^ 
like  malaria,  are  caused  by  tiny  animals.  The  causes  of  some 
diseases  have  not  yet  been  determined,  but  probably  many 
are  brought  about  independently  of  bacteria  or  parasitic 
animals.  Nevertheless,  most  of  the  common  illnesses  are  pro- 
duced by  them,  and  none  of  the  diseases  caused  by  bacteria  ever 
make  their  appearance  unless  the  germs  that  cause  them 
first  get  into  the  body  and  find  opportunities  for  growth 
there.    Any  disease  caused  by  living  germs  is  called  infectious. 

In  most  of  these  diseases  the  bacteria,  after  having  developed 
in  the  body  for  a  while,  begin  to  be  given  off  in  some  way. 
Sometimes  this  takes  place  through  the  mouth,  sometimes 
through  the  excreta,  sometimes  through  the  breath,  sometimes 
through  special  discharges  of  the  skin.  When  bacteria  are 
thus  given  off  from  the  body  of  a  sick  person,  they  are  alive 
and  active,  and  are  generally  in  condition  to  enter  the  body 
vf  another  individual  and  produce  the  same  trouble  in  him. 


FERMENTATION  AND  GERM  DISEASES  71 

Hence  one  person  can  easily  take  a  disease  from  another. 
Such  diseases  are  called  contagious. 

All  contagious  diseases  such  as  diphtheriaj  typhoid  fever, 
liiherculosis,  measles,  whooping  cough,  scarlet  fever  and  small- 
pox seem  to  be  produced  by  living  organisms,  minute  in  size 
but  capable  of  living  a  parasitic  Ufe  in  the  body,  and  passing 
readily  from  one  person  to  another.  The  germs  causing  them 
are  not  always  of  that  class  called  bacteria,  but  they  are  always 
minute,  always  parasitic  and  may  all  be  properly  classed 
as  disease  germs.  The  methods  by  which  these  germs  pass 
from  the  patient  to  the  healthy  individual  are  various.  The 
bacteria  themselves  are  not  capable  of  any  considerable 
amount  of  motion,  and  are  never  able,  of  themselves,  to  travel 
from  person  to  person.  They  must  be  carried,  and  the  various 
kinds  are  carried  by  different  means.  Some  are  carried  in  the 
air,  some  by  water  and  some  by  insects. 

Some  diseases  are  very  contagious,  by  which  we  mean 
that  they  are  very  easily  *'  caught ";  and  others  are  slightly 
contagious.  This  really  refers  to  the  ease  with  which  the  germs 
can  be  carried  from  person  to  person  and  taken  into  the  body. 
In  cases  where  the  germs  must  pass  into  the  water  and  be  sub- 
sequently drunk  before  they  can  enter  the  body  of  another 
individual,  it  is  evident  that  the  liability  of  contagion  is  less 
than  in  the  cases  where  they  simply  pass  into  the  air  and  are 
breathed  in  by  a  second  individual.  All  such  diseases  are 
infectious,  but  not  all  are  necessarily  contagious.  A  study  of 
methods  of  transmission  will  give  us  valuable  information  as  to 
ways  of  preventing  contagion. 

IMMUNITY 

Almost  all  kinds  of  bacteria  are  harmless  even  if  they  do 
get  into  our  bodies.  This  means  that  they  are  not  able  to 
multiply  in  the  body  so  extensively  as  to  produce  trouble. 
We  are  immune  against  them.  Moreover,  certain  kinds  of 
bacteria  can  grow  in  some  of  the  lower  animals  and  produce 


72  ADVANCED  PHYSIOLOGY 

trouble  there,  though  the  same  sort  cannot  injure  man. 
Further,  it  is  well  known  that  some  people  ''catch"  diseases 
more  easily  than  others.  Some  people,  indeed,  although 
again  and  again  exposed  to  diseases,  do  not  take  them, 
while  others  under  the  same  conditions  take  them  easily 
enough. . 

Lastly,  in  the  case  of  some  diseases,  such  as  scarlet  fever, 
mumps  and  whooping  cough,  if  a  person  has  them  once  and 
recovers,  he  is  not  likely  to  have  them  again  even  though 
exposed  to  them.  Such  persons  are  immune  against  a  second 
attack  of  these  diseases.  Immunity  is  a  condition  which 
enables  a  person  to  resist  diseases  when  exposed  to  them.  The 
greater  one's  power  to  withstand  diseases,  the  more  secure 
is  his  health. 

There  are  various  methods  by  which  immunity  can  be 
produced;   one  factor  only  need  be  mentioned  here. 

Resisting  power  varies  with  the  physical  condition  of  the  per- 
son. One  in  good  health,  with  strong  vitality,  is  less  liable  to 
take  the  germ  diseases  than  one  who  is  less  robust  and  vigorous. 
Out-of-door  life,  and  the  eating  of  wholesome  foods  are,  thus, 
among  our  greatest  safeguards  against  them.  Especially 
has  it  been  shown  that  alcohol  tends  to  lower  this  power  of 
resistance,  and  persons  addicted  to  the  use  of  alcoholic  bever- 
ages are  more  liable  to  yield  to  the  attack  of  infectious  dis- 
eases than  are  those  who  refrain  from  their  use.  The  reasons 
for  this  are  not  wholly  known.  It  is  certain  that  alcohol 
is  primarily  a  poison,  acting  directly  upon  the  living  cells 
so  as  to  interfere  with  their  normal  functions.  Resistance  to 
disease  is  dependent  upon  the  activities  of  the  cells,  and  it 
is  natural  to  conclude  that  if  alcohol  acts  in  any  degree  as  a 
cell  poison  it  will  interfere  with  this  resisting  power.  At  all 
events,  the  facts  are  certain;  and  the  more  frequent  the  use 
of  alcohol,  the  less  is  one's  power  of  resistance  to  harmful 
bacteria. 


FERMENTATION  AND  GERM  DISEASES  73 

STERILIZATION  AND  DISINFECTION 

In  connection  with  bacteria  and  germ  diseases,  we  fre- 
quently hear  the  terms,  sterilization  and  disinfection.  To 
disinfect  means  to  treat  a  thing  in  such  a  manner  as  to  destroy 
any  micro-organisms  that  might  produce  infection  or  disease. 
If  there  were  harmful  bacteria  in  water  and  we  could  kill  them 
mthout  injuring  the  water,  evidently  the  danger  in  drinking  it 
would  be  removed.  If  a  room  has  been  occupied  for  some  time 
by  persons  suffering  with  a  germ  disease,  bacteria  may  be 
distributed  through  the  room,  on  the  floor,  ceihngs,  curtains, 
etc.,  and  other  people  who  come  to  live  in  the  room  later  will 
be  likely  to  become  infected.  If  we  can  treat  the  room  in  such 
a  way  as  to  destroy  the  bacteria,  it  may  be  rendered  safe.  This 
we  call  disinfection.  To  steriUze  any  object  means  to  kill  all 
organisms  -whether  disease-producing  or  not. 

Th^'  simplest  method  of  sterilizing  is  by  the  use  of  heat. 
All  bacteria  are  killed  by  sufficient  heat,  and  nearly  all  that 
are  liable  to  produce  disease  in  man  are  killed  by  the  heat 
of  boiling  water.  Therefore  anything  that  can  be  boiled, 
like  water  or  milk,  or  anything  that  can  be  treated  in  boiling 
water,  like  towels  or  sheets,  can  be  easily  sterilized  by  this 
means.  Water  and  milk  are  frequently  treated  in  this  way 
when  there  is  any  suspicion  of  their  infection.  When  one  is 
uncertain  as  to  how  to  sterilize  or  disinfect  suspected  articles 
it  is  wisest  to  follow  the  advice  of  health  officers,  whose 
duty  it  is  to  know  these  methods  and  their  practical  appli- 
cations. 


CHAPTER   V 
DIGESTION  OF  FOOD:  THE  MOUTH  AND  THROAT 

In  their  original  condition  most  of  our  foods  are  of  no  more 
value  to  the  body  than  are  the  trees  of  the  forest  or  the  stones 
of  the  quarry  to  the  builder,  good  as  raw 
material,  but  not  immediately  available. 
Before  they  can  be  taken  into  the  blood 
they  must  be  softened,  ground  up  into 
small  bits  and  at  least  partially  dissolved 
into  liquid  form.  This  process  is  a  long 
Fig.  35.— Scale-     ^^^   beginning,  perhaps,  when    the   food 

LIKE     CELLS    FROM         .       .         ,,         ,  j  r    xl,       u     x    T_  '11 

THE  LINING  OF  THE     ^^  m  the  hauds  of  the  butcher  or  miller, 
MOUTH  and    carried    further,    by    some    process 

of  cooking.  The  chief  part  of  this  prep- 
aration, however,  is  performed  by  the  alimentary  canal, 
whose  main  function  is  to  grind  and  dissolve  the  food  masses 
into  readiness  for  absorption.  This  process  of  disintegra- 
tion is  partly  mechanical  and  partly  chemical,  and  we  call 
it  digestion.  The  digestive  canal  is,  in  a  sense,  a  chemical 
laboratory. 

THE  MOUTH 

The  preparation  of  food  for  absorption  begins  in  the  mouth. 
The  whole  mouth  cavity  is  lined  with  a  smooth,  moist  mem- 
brane, consisting  of  cells  (Fig.  35),  which  secrete  a  transparent 
liquid  somewhat  thicker  than  water  and  called  mucus. 
Mucus  is  of  no  value  as  a  factor  in  digestion,  but  it  keeps  the 
lining  membranes  soft  and  flexible,  and  lubricates  dry  foods 

74 


DIGESTION   OF   FOOD:   THE  MOUTH 


75 


so  that  they  can  be  pushed  back  toward  the  throat  more 
easily.  This  Hving  mucous  membrane  and  the  outer  skin 
of  the  body  come  together  at  the  Hps.  They  are  much  alike 
in  structure  save  that 
the  blood  vessels 
come  nearer  the  sur- 
face in  the  mucous 
membrane  and  make 
it  look  redder. 

The  Teeth.— Back  of 
the  lips,  which  aid 
slightly  in  holding  and 
directing  the  food,  are 
the  teeth.  These,  by 
catting,  tearing  and 
grinding  the  food,  pre- 
{)are  it  for  digestion. 
Their  shapes  are  ad- 
mirably adapted  for 
this  work,  which  is 
called  mastication. 

The  teeth  of  each 
side  of  each  jaw,  begin- 
ning at  the  middle  in  front,  comprise  two  incisors,  one  canine^ 
t  wo  bicuspids  and  three  molars,  or  grinders.  The  incisors  (Fig. 
06  /)  with  chisel  edges  are  used  almost  exclusively  for  cutting 
pieces  from  large  morsels;  in  chewing  they  come  into  action 
very  little.  The  canines  (Fig.  36  C),  named  from  their  similarity 
to  the  tearing,  tusk-Hke  teeth  of  dogs,  are  of  no  great  service 
to  civiUzed  man,  who,  though  he  may  eat  fruits  without  first 
cutting  them,  usually  cuts  his  other  foods  with  knife  and 
fork.  The  bicuspids  (Fig.  36  B),  so  called  from  the  two  prom- 
inences, or  cusps,  on  their  free  ends,  are  of  use  partly  for  tear- 
ing, and  partly  for  grinding.  The  molars  (Fig.  36  M),  or  heavy, 
many-cusped  "  back  teeth,"  are  solely  for  grinding.     Their 


Fig.   36. — Showing  the  upper  jaw  of  a 
child  and  the  lower  jaw  of  an  adult 

In  the  upper  figure  Bu  indicates  the  buds  of 
the  permanent  teeth  nearly  ready  to  push  out 
the  first  set,  or  milk  teeth. 


76 


ADVANCED    PHYSIOLOGY 


position,  far  back  near  the  hinge  of  the  lower  jaw,  gives 
great  leverage;  and  being  farthest  from  the  mouth  opening 
and  nearest  the  largest  part  of  the  cheek,  room  for  their 
grinding  function  is  insured.  The  remarkable  fitness  of  each 
structure  for  its  work  is  a  striking  fact  which  may  be  no- 
ticed in  all  parts  of  the  body.  All  of  these  are  permanent  teeth. 
All  except  the  molars  are  preceded  in  childhood  by  baby  teeth 
which  are  lost  in  early  years.  Permanent  teeth  may  appear  as 
early  as  six  years  of  age,  and  since  this  is  so,  particular  pains 
should  be  taken  that  they  are  properly  cared  for  from  the  time 
of  their  first  * 'cutting  through." 

If  a  tooth  is  cut  open,  it  proves  to  be  made  of  four  kinds 
of  material.     The  outside  layer  (see  Fig.  37),  an  extremely 

hard  deposit  of  calcium  phosphate, 
is  called  the  enamel.  This  is  thick- 
est on  the  exposed  surface  of  the 
tooth,  or  crown,  and  diminishes  until, 
as  the  tooth  enters  the  gum,  it  gives 
way  entirely  to  a  softer  substance, 
the  cement.  This  cement  covers 
the  roots  and  connects  the  teeth 
firmly  with  their  sockets  in  the  jaw 
bone.  It  is  this  substance  which 
yields  when  a  tooth  is  extracted. 

Inside  the  enamel  and  cement  is  a 
uniform  layer,  the  dentine.  This, 
too,  is  calcium  phosphate  in  compo- 
sition, but  is  less  hard  than  the 
enamel.  Inside  the  dentine  is  a  space  occupying  the 
central  part  of  the  tooth,  and  extending  down  into  the 
tips  of  the  roots.  This  central  space  is  occupied  by  a  soft, 
pasty  mass,  like  the  marrow  of  a  bone,  filled  with  fatty  and 
connective  tissues,  blood  vessels  and  nerves.  These  vessels 
and  nerves  enter  the  tips  of  the  roots,  the  former  bringing 


Decoued 


Cement 


'Nerve 

Fig.    37. — A    section 

THROUGH     A     TOOTH 


DIGESTION  OF  FOOD:    THE  MOUTH  77 

nutritive  materials  for  the  tooth,  the  latter  regulating  the 
use  of  these  materials;  Figs.  36  and  37. 

Care  of  the  Teeth. — Cleaning  the  teeth  may  seem  to  be 

unnecessary,  or  merely  a  matter  of  good  form;  but  this  is  a 
wrong  idea.  In  spite  of  the  hard  nature  of  the  teeth,  they 
are  very  liable  to  decay,  as  almost  everyone  knows  to  his 
misfortune.  This  decay  is  brought  about  by  circumstances 
which  we  can  in  great  measure  prevent  if  we  understand 
them.  It  is  caused  in  part  by  the  bacteria  in  the  mouth. 
These  are  not  able  to  affect  the  uninjured  teeth  though  they 
can  readily  attack  the  softer  foods  that  may  lodge  in  or  between 
them.  If,  after  eating,  one  chances  to  leave  some  of  the  food 
in  the  crevices  between  the  teeth,  the  bacteria  at  once  begin 
to  feed  upon  it.  The  mouth  is  warm  and  moist  and  furnishes 
the  very  best  possible  conditions  for  bacterial  growth.  In  these 
particles  of  food,  therefore,  bacteria  flourish  and,  after  a  time, 
turn  them  sour  in  much  the  same  way  that  they  turn  milk 
sour.  The  sourness  is  due  to  the  production  of  an  acid,  which, 
although  not  formed  in  very  large  amounts,  always  appears 
if  food  is  left  between  the  teeth.  Upon  the  hard  substance 
of  the  teeth  this  acid  acts  at  once,  dissolving  the  lime  in  such 
a  way  as  to  produce  soft  spots  or  even  cavities.  Upon  the 
hard  enamel  the  acid  acts  only  with  difficulty,  but  if  this 
is  cracked  or  broken  the  acid  acts  easily  upon  the  softer  den- 
tine within.  As  soon  as  these  weak  spots  appear  the  teeth 
decay  rapidly;  Fig.  37.  Since  our  permanent  teeth  do  not  grow 
and  are  never  repaired  or  replaced  by  nature,  it  is  very  impor- 
tant that  they  be  kept  in  good  condition. 

It  is  becoming  more  and  more  certain  that  material  from 
decayed  teeth,  or  from  pus  cavities  in  or  above  their  roots, 
may  cause  very  unexpected  and  serious  results,  e.  g.  nervous- 
ness, epilepsy,  indigestion,  blindness,  or  even  insanity.  **Mouth 
cleanliness'*  is  of  the  greatest  importance. 

What  is  the  use  of  toothache  ?  Though  unpleasant,  it  certainly 


78 


ADVANCED  PHYSIOLOGY 


tells  one  that  he  is  not  treating  his  teeth  properly  since  a  tooth- 
ache generally  means  decay.  If  one  avoids  injuring  the  en- 
amel with  hard  substances,  and  if  he  does  not  allow  food  to 
remain  between  the  teeth  for  the  bacteria  to  act  upon,  he  can 
thus  check  the  pro'cess  of  decay.  Carbohydrate  foods  are  most 
liable  to  be  turned  acid  by  bacteria,  and  hence  bits  of  cracker 
or  bread  are  among  the  worst  materials  to  leave  lodged  in 
the  mouth. 

When  a  tooth  begins  to  decay,  the  dentist  removes  the 
decaying  portion;  he  then  closes  the  opening  with  gold  or 
silver  or  some  other  hard  material.  It  is  extremely  important 
to  have  a  cavity  attended  to  when  it  is  very  small  so  as  to 

save  the  tooth;    hence   the 


Papiltoe  with  taste  buds 


Tbns'if 


teeth  should  be  examined 
by  a  dentist  at  least  twice 
a  year.  This  is  not  only 
necessary  as  a  means  to  uni- 
form health,  but,  contrary  to 
the  belief  of  some,  is  much 
the  most  economical  custom 
for  every  one. 


The  Tongue. — The  tongue 
is  a  mass  of  muscles  whose 
fibres  can  move  it  in  differ- 
ent ways,  either  guiding 
the  food  in  the  process 
of  chewing  or  carrying 
the  food  back  toward  the 
gullet.  On  the  upper  surfaces  of  this  organ  are  numer- 
ous minute  projections,  or  papillse;  Fig.  38.  Everyone  has 
noticed  the  very  rough  tongues  of  dogs  and  cats.  On  the  hu- 
man tongue  are  three  kinds  of  papillse.  The  largest,  called 
the  circumvallate,  are  few  in  number  and  at  the  very  back  of 
the  tongue;  Fig.  38.     These  papillae  are  short  and  blunt  in 


Tig. 


-The    surface 

TONGUE 


OF      THE 


DIGESTION  OF  FOOD:  THE  MOUTH 


79 


Openincj 


To sM  Cells 


structure,  growing  up  from  shallow  pits  in  the  tongue^s  surface- 
More  numerous  than  these  and  scattered  over  the  remainder 
of  the  tongue  are  two  types,  the  filiform  and  the  fungiform 
papillae.  As  the  terms  indicate,  the  former  are  slender  and 
thread-like;  the  latter  are  short,  pillar-like  growths.  In  the 
tissues  of  the  circumvallate  and  fungiform  papillae  are  located 
the  organs  of  taste,  the  so-called  taste  buds.  The  cells  making 
up  these  buds  are  elongate,  arranged  in  a  more  or  less  spherical 
mass.  The  cells  in  the  middle  of  this  mass  come  close  to  the 
surface  and  are  affected  by  the 
food  which  touches  them;  Fig.  39. 
From  them  the  stimulus  passes 
through  nerves  to  the  brain. 

There  is  a  kind  of  taste  geog- 
raphy mapped  out  on  the  tongue's 
surface.  Bitter  tastes  are  noticed 
at  the  back  of  the  tongue,  acid  on 
the  sides,  salt  and  sweet  toward 
the  front.  None  of  these  tastes  can 
be  perceived  if  the  tongue  be  wiped 
dry.  In  other  words,  all  material 
to  be  tasted  must  be  in  solution.* 
Electric  stimuli  applied  to  the 
tongue  produce  the  same  impres- 
sion as  dissolved  foods.  Thus 
arises  the  popular  contention  that 

electricity  is  sweet,  for  the  wires  are  usually  applied  to  that 
portion  in  which  the  sweet-perceiving  nerve  endings  are 
located. 

The  Palate. — The  roof  of  the  mouth  toward  the  front  is 
called  the  hard  palate  and  contains  a  bony  partition  between 
the  mouth  and  nose  chambers.  This  bony  partition,  however, 
soon  ends,  and  the  palate  continues  backward  toward  the 
throat  as  a  soft  membrane;   Fig.  40.    This  soft  palate  extends 

*  Students  should  prove  these  statements  by  experiments  at  home. 


Fig.  39. — A  taste  bud  from 

THE  TONGUE 
Highly  magnified,  showing  the 
taste  cella. 


80 


ADVANCED  PHYSIOLOGY 


to  the  place  where  the  nose  and  mouth  cavities  come  together 
to  form  the  throat  or  pharynx.  From  the  back  edges  of  the 
soft  palate,  just  in  the  middle,  hangs  down  the  uvula,  a  ver- 
tically placed  piece 
of  connective  tissue 
and  muscle,  half  an 
inch  long  and  about 
a  quarter  of  an  inch 
thick.  The  uvula 
sometimes  becomes 
swollen  and  elon- 
gated until  it  hangs 
down  on  the  tongue 
and  even  into  the 
throat.  It  then  pro- 
duces  a  slight  tick- 
ling which  excites  a 
cough.  A  physician 
sometimes  cures  dis- 
eases   of    the   throat 


-^Tonsil 
GloHis 
Oesophagus 


Sptn<JCord'-''' 

Fig.  40. — A  section  through  the  head 

Ehowingasurface  view  of  the  biain,  and   the  mouth     by  removing    a    piece 
and  nasal  cavities.  ^f  ^Jie  UVUla. 

In  these  days  of  hurry  and  stress,  too  much  emphasis  cannot 
be  placed  on  the  necessity  of  thoroughly  chewing  the  food. 
If  swallowed  in  large  pieces,  only  the  surface  of  these  will 
easily  dissolved. 

DIGESTION  IN  THE  MOUTH 

While  food  is  being  crushed  into  small  pieces  by  the  teeth 
it  is  mixed  with  the  liquids  in  the  mouth  until  thoroughl; 
moist.  The  membranes  of  the  mouth  are  kept  wet  by 
a  mucous  fluid  that  exudes  from  their  surfaces  and  is 
mixed  with  the  food,  upon  which  it  really  has  no  special 
effect.  As  soon  as  the  food  enters  the  mouth  and  in- 
deed,  sometimes    before — for    the    mere    sight    of    food    or 


DIGESTION  OF  FOOD:  THE  MOUTH 


Si 


Fig.  41.- 


Arterif 
Diagram 


Showing  the  positions  of  the 
parotid  and  submaxillary 
glands. 


even  the  thought  of  it  produces  the  same  effect — a  watery 
liquid,  the  saliva,  begins  to  be  poured  into  the  mouth. 
This  comes  from  three  pairs  of 
salivary  glands.  1.  The  parotid, 
j  ust  below  and  in  front  of  each  ear, 
with  long  ducts  opening  through  the 
sides  of  the  mouth  opposite  the 
second  molar  teeth.  2.  The  sub- 
lingual, beneath  the  tongue,  with 
numerous  separate  ducts.  3.  The 
submaxillary,  beneath  the  tongue, 
on  each  side,  near  the  angle  of  the 
jaw;  Fig.  41.  The  ducts  of  these 
last  open  under  the  tongue,  on  each 
side  of  the  middle,  toward  the  front, 
on  slight  elevations. 

These  salivary  glands  are  com- 
pact masses  of  varying  sizes.      The 

parotids  are  fiat  and  of  almost  the  same  area  as  the  ear; 
the  submaxillaries  are  about  the  size  of.  a  walnut.  Under  a 
microscope  they  are  found  to  consist  of  many  minute  cavities. 
If  one  imagines  a  cluster  of  extremely  small  grapes,  which  are 
hollow,  and  discharge  sap  into  their  stems,  he  will  get  a  good 
picture  of  the  structure  of  such  a  gland;  Fig.  42.  Each  spher- 
ical cavity  (or  each  grape  in  the  illustration)  is  called  an 
alveolus,  and  each  has  its  walls  made  of  cells.  The  cells 
extract  from  the  blood  material  out  of  which  they  make 
saliva;  this  they  pour  into  a  little  duct  which  drains  the 
alveolus.  Each  duct  joins  others  from  other  alveoli,  and  all 
finally  unite  to  form  a  single  duct  which  carries  the  secretion 
into  the  mouth.  These  little  clusters  of  hollow  sacs  are  micro* 
scopic,  very  numerous,  and  all  bound  together  into  a  compact 
mass.  Several  other  glands  in  the  body  are  constructed  on 
the  same  plan,  and  this  pattern  is  called  racemose  from  a 
Latin  word  that  means  "  full  of  clusters." 


m 


ADVAN€EB    PHYSIOLO^IY 


0 

the 


The  salivary  glands  really  receive  stimuli  from  the  brain. 
The  taste  of  food  starts  a  nerve  impulse  that  goes  to  the  brain; 
there  certain  nerve  centers  are  excited  and  from  them  another 
impulse  passes  to  the  salivary  glands,  causing  them  to  se- 
crete saliva.     This  passage  of 
the   impulse   from    the   brain 
to   the   glands  is   an   uncon- 
scious one,  and  we  certainly 
do  not  secrete  saliva  by  any 
volition  of  our  own.    Such  an 
action  is  called  a  reflex  action. 

Saliva  is  more  than 
water.  This  moistens 
food  and  makes  it  easy  to 
swallow.  Indeed,  this  is  one 
of  the  most  important  func- 
tions of  saliva.  One  cannot 
swallow  a  dry  cracker  until 
he  has  thoroughly  wet  it  with 
saliva  or  water.  When  people  are  much  frightened  their  sali- 
vary glands  sometimes  refuse  to  secrete  and  at  such  times 
they  find  it  difficult  or  impossible  to  swallow. 

While  this  is  a  very  important  function,  saliva  has  also 
a  digestive  action  on  the  food.  This  is  due  to  an  enzyme  called 
ptyalin,  present  only  in  very  minute  quantity,  but  having 
a  powerful  effect  on  starch,  which  it  converts  into  sugar. 
This  change  is  absolutely  necessary,  since  starch  unchanged 
cannot  be  absorbed  from  the  digestive  tract  and  hence  cannot 
be  used  in  the  body.  The  conversion  of  starch  into  sugar,  as 
we  have  already  noticed,  is  brought  about  by  the  addition  of 
water  to  starch.  (See  page  63.)  But  this  combination  will  not 
occur  except  under  the  influence  of  some  outside  agent  such 
as  ptyalin.  Sugar  is  a  substance  that  is  easily  absorbed 
through  the  intestine  while  starch  cannot  be  absorbed  at  all. 
Hence  this  change  from  starch  into  sugar  is  true  digestion. 


Fig.  42. — Showing  the  structure 
of  a  salivary  gland 

A ,  moderately  magnified  and  represent- 
ed as  less  compact  than  in  reality,  B, 
two  alveoli,  highly  magnified  and  show- 
ing the  connection  with  the  duct. 


DIGESTION  OF  FOOD:   THE  MOUTH  83 

In  eating,  food  is  usually  kept  for  so  short  a  time  in  the 
mouth,  is  so  imperfectly  chewed  and  broken  up  that  the 
ptyalin  solution  acts  upon  only  a  small  portion  of  the  starch. 
Saliva  does  not  at  all  affect  other  foods,  i.e.  fats  or  proteids. 
In  its  chemical  reaction  it  is  slightly  alkaline,  due  to  traces 
^of  inorganic  salts.  Ptyalin  will  not  act  at  all  if  the  food  mass 
is  acid,  as  when  it  is  mixed  with  vinegar. 

THE  THROAT  / 1      ;^ 

The  Pharynx. — Back  of  the  mouth  and  partly  shut  off 
from  it  is  a  considerable  cavity  called  the  pharynx,  or  throat, 
through  which  food  must  go  before  it  reaches  the  gullet; 
Fig.   40.    In  a  person  of  average  .*. 

size  this  cavity  is  about  four  and     fjif  '^-c///^? 

a  half  inches   in   length    and   of      !-i'..v*  '1 

varying  width. 

It  is  partly  shut  off  from  the 
mouth  by  the  tongue  below,  by 
the  soft  palate  and  uvula  above, 
and  by  the  pillars  of  the  fauces     Fig.  43.— Ciliated  cells  that 

,      ,,  .,  rnt,  1       i.  LINE  THE  PHARYNX 

at  the  sides.     These  last  are  ver- 
tically   placed    folds   of  tissue  which  can  be  easily  seen  by 
opening    the    mouth    widely    before    a    mirror.      They    are 
somewhat  like   thick   curtains   hanging  down  at  the  sides  of 
the  opening  into  the  throat. 

The  Tonsils. — To  one  who  thinks  that  there  is  a  use  for 
everything  in  the  world,  it  is  interesting  to  find  that  there 
are  several  structures  in  the  human  body  which  are  appar- 
ently of  no  value.  Among  these  are  the  tonsils,  which  are 
frequently  removed  by  a  slight  surgical  operation.  These 
growths  are  located  on  each  side  of  the  passage  from  the 
mouth  to  the  throat,  one  between  each  pair  of  the  pillars  of 
fauces;  Fig.  40.  They  vary  much  in  size,  though  in  most 
cases  they  are  about  as  large  as  half  a  walnut.  From  their 
position  they  are  much  exposed  tQ  currents  of  air  taken  iu 


84  ADVANCED    PHYSIOLOGY 

through  the  nose  or  mouth,  and  thus  easily  become  inflamed 
by  excessive  cold,  or  by  foreign  particles  in  the  air. 

There  are  other  openings  into  the  pharynx  besides  that  from 
the  mouth;  of  these,  two  open  from  the  nose  just  above  the 
soft  palate,  near  the  mid-line.  At  this  upper  end  where 
the  nasalpassages  enter,  the  pharynx  cavity  is  not  very  large 
and  is  roofed  over  by  the  lower  bone  of  the  brain  box,  covered 
by  a  soft  membrane.  Into  this  part  of  the  pharynx  project 
innumerable  hair-like  structures,  called  cilia;  Fig.  43.  These 
cilia  are  minute,  transparent  filaments  which  have  the  power 
of  lashing  to  and  fro  and  creating  a  current  in  the  mucus 
on  the  surface  of  the  cells.  Particles  of  dust  may  thus  be 
moved  along,  and  tears,  which  run  down  into  the  nose  canals, 
may  also  be  hurried  to  the  pharynx,  where  one  becomes  con- 
scious of  the  liquid  and  spits  it  fiom  the  mouth  or  swallows  it. 

These  dust  particles  in  the  air  are  generally  covered  with 
bacteria;  and  since  the  tonsils  are  deeply  wrinkled,  these  bacteria 
easily  lodge  in  the  crevices  and  provoke  inflammation.  It  has 
even  been  proven  that  80%  of  diseased  tonsils  harbor  the 
type  of  bacteria  which  causes  tuberculosis,  and  may  thus 
act  as  an  entrance  point  for  this  most  serious  malady. 

In  the  upper  part  of  the  pharynx  cavity  on  each  side  is  a 
minute  opening  through  which  a  bristle  can  be  thrust  into  a 
canal  leading  to  the  ear.  These  small  passages  are  called  the 
Eustachian  tubes,  and  have  much  to  do  with  hearing;  Fig.  40. 

If  one  closes  the  nose  passages  by  holding  the  nose  between 
the  fingers,  and  then  swallows,  the  noise  in  the  ears  shows  that 
a  passage  exists  between  them  and  the  throat.  When  the 
pharynx  wall  is  sore  and  swollen  (pharyngitis) ,  this  canal  may 
become  closed  and  a  disagreeable  noise  be  constantly  heard. 

At  the  lower  end  of  the  pharynx  are  two  comparatively 
large  openings.  The  front  one  is  the  glottis,  which  is  the  upper 
end  of  the  windpipe,  and  leads  to  the  lungs;  the  one  behind 
that  is  in  the  gullet,  or  oesophagus  opening,  and  leads  to  the 
stomach.     It  is  evident,  then,  that  all  food  which  leaves  the 


DIGESTION    OF    FOOD:  THE    MOUTH  85 

mouth  on  the  way  to  the  stomach  must  pass  over  the  upper 
end  of  the  windpipe. 

There  are,  therefore,  seven  openings  into,  or  out  of  the 
pharynx,  all  of  which  may  be  closed.  The  large  passage  from 
the  mouth  may  be  closed  by  the  tongue,  the  soft  palate  and  the 
pillars  of  fauces,  all  of  which  contain  muscles;  the  Eustachian 
tubes  can  be  closed  by  muscles  going  around  the  tubes  and  by 
the  pressure  of  surrounding  tissues;  the  glottis,  by  a  lid-like 
door,  the  epiglottis,  which  drops  back  over  the  opening  when 
anything  is  swallowed;  and  the  oesophagus  may  be  closed 
through  the  contraction  of  muscles  which  pass  circularly 
around  it.  The  entrance  from  the  nose  passages  is  less  per- 
fectly shut  off  than  the  others  and  less  often;  but  it  can  be 
closed  by  the  raising  of  the  curtain-like  soft  palate  and  the 
general  contraction  of  the  muscles  in  the  upper  part  of  the 
pharynx.  One  or  the  other  of  these  openings  may  be  closed  ac- 
cording to  whether  food  or  air  is  passing  through  the  cavity. 

DISEASES  OF  THE  MOUTH  AND  THROAT 

Tonsilitis. — We  have  already  noticed  that  the  mouth  usually 
contains  microscopic  germs,  called  bacteria.  Ordinarily  these 
do  no  harm,  but  occasionally  bacteria  of  a  more  malignant 
type  get  into  the  mouth  and  produce  trouble. 
They  sometimes  attack  the  tonsils  or  the*  roof 
and  walls  of  the  mouth  and  throat,  causing 
inflammation;  the  result  is  first  noticed  as  a 
sore  throat,  which  may  merely  have  an  appear-  Fig.  44. — 
ance  of  redness  that  soon  disappears.  If  the  Bacteria 
throat  is  covered  with  white  patches,  however,  (Strepto- 
and   the   tonsils    are    swollen    and    painful,   the      ?^^,     . 

Found       m 

trouble    is    called  tonsilitis;    Fig.   44.       This    is     cases  of  ton- 
accompanied    by   fever  and    a    general  feeling  of      ^^^'*^^- 
illness;  but  it  is  not  likely  to  be  serious,  and  with  proper  treat- 
ment will  soon  pass  away.      If  the  inflammation  becomes  still 
greater,  and  the  surrounding  tissues  are  distended  with   pus, 


Fig.    45.— 


^  ADVANCED  PHYSIOLOGY 

making  it  almost  impossible  to  swallow,  it  is  called  quinsy 
sore-throat,  which  also  yields  to  proper  treatment. 

Diphtheria. — Diphtheria  has  been  one  of  the  most  serious 
of  human  diseases  and  one  which  frequently  results  fatally. 
It  is  produced  by  bacteria  (Fig.  45.)  which  cause  the  formation 
of  white  patches  on  the  tonsils  and  near-by  surfaces.    These 
•  spread  and   grow   together,    finally   forming   a 

js\  membrane  over  the  throat  which  may  extend 

*^  ^  down    into    the    windpipe    and   interfere   with 

breathing.      Until    recently     no    remedy    for 
diphtheria  was  known,  and  no  disease  excited 
greater    apprehension.      Within    the    past  feWj 
(Bacterium   7^^^^,   however,   bacteriologists    have    found 
diphtheria)    method  of  treating  it  successfully  by  the  us< 
The   cause  of   of   a   substance  called  antitoxin  which  neutral- 
diphtheria.        -^gg    ^^^    g^g^^    Qf   ^j^g  bacteria.      This    anti- 
toxin is  prepared  from  the  blood  of  horses  which  have  previ- 
ously been  treated  with  diphtheria  poisons.     By  its  use,  the 
number  of  deaths  from  diphtheria  has  been  much  reduced. 
It  is  better,  however,    to    use  the   antitoxin   in   the    early 
stages  of  the  disease.      Therefore,  it  is  important  to  attend 
promptly  to  all  cases  of  sore  throat,  and  a  physician  should  be 
called  whenever  it  becomes  serious  or  when  white  spots  appear. 
Both  tonsilitis  and  diphtheria  are  very  contagious.     The 
bacteria  in  the  throat  pass  out  into  the  air  when  the  patieni 
coughs  or  speaks  loudly,  and  they  are  also  sure  to  get  upoi 
any  object  that  the  patient  places  in  his  mouth.     Knives,^ 
forks  and  spoons  used  in  eating,  pencils  which  he  may  place^ 
in  his  mouth,  books  handled  by  the  patient  are  all  liable  tc 
be  covered  with  the  germs.     Such  articles  will  obviously  be 
a  source  of  contagion  to  others  who  use  them,  but  if  the 
articles   are  boiled,  when  possible,  for  ten  minutes  in  water 
this  danger  may  be  removed. 

The  serious  nature  of  diphtheria  and  its  frequency  among 
children  has  led  to  the  custom  of  keeping  from  school  those 


DIGESTION   OF   FOOD:  THE   MOUTH  87 

who  have  had  the  disease  until  the  germs  have  disappeared 
from  their  throats;  sometimes  other  children  from  the  same 
family  are  kept  at  home,  in  quarantine  as  it  is  called,  to  pre- 
vent them  from  carrying  the  germs  to  others  in  school.  In 
all  cases  the  patient  should  be  isolated;  that  is,  he  should  be 
kept  in  a  room  by  himself  and  no  one  should  be  allowed  to 
see  him  except  physicians  and  nurses.  By  such  means  the 
spread  of  the  germs  can  be  prevented  and  many  lives  saved. 
So  dangerous  is  this  disease  that  any  precaution  which  will 
prevent  its  dissemination  is  justifiable. 

Mumps. — Mumps  is  another  disease  of  the  organs  around 
the  mouth,  being  primarily  a  swollen  condition  of  the  parotid 
glands.  The  face  swells  on  one  or  both  sides,  swallowing  is 
painful,  and  for  a  day  or  tw^o  the  patient  is  very  uncomfort- 
able. The  cause  of  the  trouble  is  not  known,  and  it  usually  soon 
passes  away.  It  is  a  contagious  disease  and  can  be  avoided  by 
keeping  away  from  those  having  it,  but  a  person  rarely  has  it 
more  than  once. 

Whooping  Cough. — Whooping  cough  is  a  disease  charac- 
terized by  violent  paroxysms  of  coughing.  It  is  believed  to  be 
caused  by  a  bacterium  that  clings  in  the  air  passage.  The 
disease  is  certainly  contagious,  and  is  easily  caught  by  another 
person  when  the  patient  is  coughing.  At  such  times  the  germs 
are  scattered  from  the  patient  and  may  find  their  way  into 
another  person  in  the  vicinity.  The  only  method  of  avoid- 
ing the  germs  is  by  keeping  away  from  those  who  have  the 
disease,  and  especially  by  avoiding  their  breath  at  times  of 
coughing.  The  chance  of.  contagion  by  other  means  is  slight 
and,  while  the  safest  plan  is  to  avoid  patients  entirely,  a  per- 
son may  frequently  associate  with  one  who  has  the  disease 
without  catching  it,  if  he  is  careful  to  avoid  the  breath.  As  long 
as  the  coughing  continues,  usually  several  weeks,  the  danger 
of  contagion  remains;  although  it  decreases  in  the  later  stages 
of  the  disease.  Whooping  cough  is  chiefly  a  disease  of  children 
although  adults  frequently  have  it.    Second  attacks  are  rare. 


CHAPTER    VI 

DIGESTION  OF  FOOD:  THE  (ESOPHAGUS  AND  STOMACH 

Connecting  the  pharynx  and  the  stomach  cavities  is  a 
tube  about  ten  inches  in  length  called  the  oesophagus. 
This  tube  is  lined  throughout  by  an  epithelium  secreting 
mucus,  and  for  this  reason  it  offers  little  resistance  to  the 
swallowing  of  food. 

Swallowing. — After  food  has  been  masticated  and  moist- 
ened by  the  saliva  it  is  rolled  up  by  the  tongue  into  a  smooth, 
moist  mass.  The  tongue  is  then  pushed  up  against  the  roof 
of  the  mouth,  first  at  its  tip,  and  then  moved  backwards; 
the  food  ball,  being  moist,  slips  along  easily  and  is  pushed 
through  the  opening  into  the  throat.  Up  to  this  point  the 
process  of  eating  has  been  under  one's  control  and  could  have 
been  stopped  at  any  moment;  but  as  soon  as  food  goes  into 
the  throat  it  passes  beyond  voluntary  management.  If  one 
should  discover  at  this  moment  that  the  food  contained 
poison  he  could  not  refrain  from  swallowing  it,  for  from  this 
point  the  action  is  involuntary,  i.e.  cannot  be  governed  by 
one's  will  power. 

''How  can  a  man  standing  on  his  head  drink  water,  or  a 
cow  drink  out  of  a  brook  when  her  head  is  so  much  lower 
than  her  stomach?"  This  question  is  easily  answered  as 
soon  as  we  understand  the  action  of  the  oesophagus.  Two 
coats  of  muscle  are  found  in  the  wall  of  the  tube;  next  to 
the  lining  is  a  layer  of  muscle  going  around  it,  and  outside 
this  is  a  layer  running  lengthwise.  By  the  combined  action 
of  these  a  "  swallow,"  or  bolus,  of  food  is  pushed  downward, 
the  muscles  in  front  of  the  food  mass  continually  letting  the 

88 


DIGESTION  OF  FOOD:  THE  (ESOPHAGUS 


passage  open  up,  while  those  behind  the  mass  contract  and 
thus  push  it  along.  The  result  is  much  the  same  as  when  one 
forces  a  slippery  ball 
through  a  rubber 
tube  by  squeezing 
the  tube  between  the 
thumb  and  finger  be- 
hind the  ball.  This 
action  on  the  part  of 
the  muscles  would, 
of  course,  carry  food 
along  the  tube,  no 
matter  what  the  po- 
sition of  the  body. 
Even  water  does  not 
run  down  the  gullet;  it 
is  pushed  down,  grav- 
ity having  little  or 
nothing  to  do  with  the 
process.  This  pecu- 
liar method  of  move- 
ment, called  peristal- 
sis, occurs  through- 
out the  entire  alimen- 
tary canal.  In  man,  a  wave  passes  from  the  pharynx  to  the 
stomach  in  about  six  seconds. 

BODY  CAVITY  AND  ITS  SUB-DIVISIONS 

All  the  space  inside  the  ribs  and  the  body  wall,  from  the 
hips  to  the  shoulders,  is  called  the  body  cavity.  This  is  not 
all  in  one  large  space,  but  is  divided  into  an  upper  and  a 
lower  part  by  a  horizontal  partition,  called  the  diaphragm; 
Fig.  46.  At  its  center  this  is  a  thin  sheet  of  tendinous  material 
from  the  edges  of  which  muscles  radiate  to  the  body  wall; 
it  extends  across  the  body  cavity  betweeu  the  ribS;  backbone 


Abdomen 


Fig.  46. — Showing  the  body  cavity  divided 
by  the  diaphragm  into  thorax  and  ab- 
DOMEN 


90  ADVANCED  I'HYSIOLOGY 

and  breast-bone,  about  one-third  of  the  way  down  from  the 
shoulders;  see  Fig.  46.  The  upper  and  smaller  cavity  is  called 
the  chest,  or  thorax,  and  its  principal  contents  are  the  heart 
and  lungs.  The  lower,  larger  space  is  the  abdominal  cavity, 
which  contains  the  stomach  and  intestine,  the  large  glands 
connected  with  them,  and  the  spleen,  kidneys  and  bladder. 

There  are  irregular  crevices  and  spaces  between  these  organs, 
but  these  are"  perfectly  filled  with  the  body  cavity  fluid 
{coelomic  fluid) . 

Nearly  all  these  organs  have  some  muscular  tissue  in  their 
walls  and  are  continually  going  through  movements;  or  if 
they  are  themselves  quiet,  they  are  being  constantly  rubbed 
against  by  neighboring  organs  which  are  in  motion.  This 
would  result  in  a  large  amount  of  friction  and  irritation,  if 
it  were  not  for  the  secretions  of  the  serous  membrane,  which 

forms  a   delicate    lining    to    both 
the  thoracic  and  abdominal  cav- 
ities.    This  lining  in  the  thoracic 
cavity  is   called  the  pleura;    that 
of  the  abdominal  cavity  is  known 
as  the  peritoneum;  Fig.  47.    Along 
certain  lines,  this  lining  is  raised 
into  folds  which  hang  out  into  the 
cavities    and    in    these    folds    the 
Fig.  47.— Diagrammatic  sec-    organs    are    held.      One   particular 
TioN  ACROSS  THE  ABDOMEN      fold  of  the  perltoueum,  called  the 
Showing  the  relation  of  the  peri-   mescntery,  is  especially  large  and 

toneum  and  mesentery.  •"  ,i      •  .  rm  • 

holds  the  small  mtestme.  This 
complex  lining  is  composed  of  one-celled  glands,  constantly 
secreting  a  colorless  fluid  which  allows  the  organs  to  glide  easily 
over  one  another  or  against  the  walls  of  the  cavity. 

THE  STOMACH 

The  oesophagus  extends  down  through  the  thorax  as  a 
nearly  straight  tube,  passing  through  the  diaphragm,  after 


DIGESTION  OF  FOOD:  tHE  (ESOPHAGUS 


01 


tardioc  Valve 


which  it  enlarges  into  a  good  sized  organ,  the  stomach,  lying 
a  little  to  the  left  of  the  middle  line;  Fig.  46.  The  stomach 
is  pear-shaped  and  lies  with  the  small  end  pointing  obliquely 
downward,  and  to  the  right.  When  moderately  full  it  is 
about  ten  inches  long,  by  four  wide  and  deep,  and  holds  about 
three  pints.  The  entrance  of  the  oesophagus  is  on  the  upper 
side,  about  the  middle  of  its  length,  and  is  commonly  closed 
by  a  muscular  ring, 
the  cardiac  valve; Fig. 
48.  This  prevents  the 
food  from  going  up 
the  oesophagus  again, 
while  the  stomach  is 
contracting  about  it. 
Sometimes,  when 
there  is  too  much 
food  in  the  stomach, 
or  when  the  food  does 
not  digest  well,  this 
valve  opens  and  a  re- 
versal of  the  muscu- 
lar action  forces  the 
food  back  through 
the  oesophagus  to  the 
mouth.  This  is  vomiting  and  occurs  most  frequently  in  babies, 
in  which  case  the  cause  is,  generally,  too  much  food.  With 
adults,  vomiting  and  nausea  usually  occur  only  when  the 
stomach  is  disturbed  by  food  which  does  not  properly  digest. 

From  the  small  end  of  the  stomach,  called  the  pyloric  end, 
starts  the  first  section  of  the  intestine,  the  opening  into  it 
being  guarded  by  the  strong,  circular,  muscular  pyloric 
valve;   Fig.  48. 

The  cavity  of  the  human  stomach  is  one  continuous  space, 
though  in  some  lower  animals  which  ''  chew  the  cud,"  as  we 
3ay,  there  are  four  divisions  in  it;    Fig.  49.     In  the  camel, 


Fig.  48. — Diagkam   of  the  stomach  and 
intestine  laid  open 

Showing  the  relation  of  ducts  of  liver  and  pancreas 
to  one  another  and  to  intestine. 


92 


ADVANCED  PHYSIOLOGY 


Fig.  49. — The  stomach  of  a  sheep 

Showing  the  four  compartments,  (Huxley) 


too,  numbers  of  sac-like  outgrowths  from  the  stomach  are 
provided,  in  the  cavities  of  which  water  is  stored  to  be  used 

when  the  animal 
Oetophoifus  ^^^*^»T*^  needs  it.  On  the  ex- 
terior of  the  human 
stomach  is  a  moist 
covering  which  is, 
in  reality,  continuous 
with  the  mesentery 
in  which  the  intes- 
tine is  swung.  Inside 
this  are  three  sets  of  muscle  fibres,  longitudinal,  circular  and 
oblique,  and  separated  from  the  lining  of  the 
stomach  by  a  thin  layer  of  fat,  the  function  of 
which  cannot  be  definitely  stated. 

Next  comes  the  stomach  lining  proper.  If  this  is 
seen  when  the  stomach  is  empty,  there  appears  to 
be  a  series  of  wrinkles  or  folds,  going  lengthwise 
of  the  organ,  from  the  pyloric  to  the  cardiac 
regions;  these  folds  are  spoken  of  as  rugae; 
Fig.  48.  Furthermore,  if  any  part  of  the  inner 
wall,  on  or  between  the  folds,  were  to  be 
examined  with  a  lens,  the  appearance  would  be 
that  of  innumerable  tiny  pits,  of  polygonal 
shape,  giving  to  the  whole  the  semblance  of  an 
extremely  fine  celled  honey-comb.  These  pits 
are  scarcely  over  one  one-hundredth  of  an  inch 
in  diameter,  and  in  the  bottom  of  each  is  a 
minute  opening  through  which  gastric  glands 
pour  a  secretion.  The  glands  are  short  and 
cylindrical,  thousands  in  number,  and  can  be 
compared  to  tiny  tubes  lying  side  by  side,  with 
their  mouths  opening  into  the  stomach  cavity; 
Fig.  50.  Each  of  these  glands  is  lined  with 
large  cells  which   make  gastric   juice    from    the 


Fig.  50.— a 

SINGLE 
GASTRIC 
GLAND 
Veiy  highly 
magnified 


DIGESTION  OF  FOOD:  THE  (ESOPHAGUS  93 

blood  that  flows  around  them,  and  pour  it  into  the  cavity 
of  the  gland,  whence  it  flows  into  the  stomach. 

COMPOSITION  AND  ACTION  OF  THE  GASTRIC  JUICE 

Water  makes  up  over  99%  of  the  gastric  secretion.  Of 
the  remainder  0.3%  is  pepsin,  0.2%  hydrochloric  acid  and 
0.1%  sodium  chloride  (common  salt).  Less  in  quantity,  but 
important,  are  the  two  ferments  rennin  and  gastro-lipase ; 
The  work  of  the  gastric  juice  is  two-fold.  1.  It  softens 
the  solid  foods,  which  are  consequently  easily  broken  up  into 
shreds  by  the  active  churning  motion  of  the  stomach.  Meat, 
for  example,  is  made  up  of  great  numbers  of  little  fibres 
bound  together  into  a  solid  mass  by  connective  tissue.  This 
tissue  is  dissolved  away  by  the  gastric  juice,  thus  setting 
free  the  fibres  and  allowing  the  liquids  to  act  further  on 
each  separate  fibre.  The  fat  of  the  meat  is  also  set  free  from 
the  masses  in  which  it  is  swallowed,  and  is  melted  by  the 
heat  of  the  body  into  oil.  This  softening  action  is  performed 
chiefly  by  the  acid  and  water  of  the  gastric  secretion,  not  by 
the  pepsin. 

We  shall  presently  see  that  all  foods  are  digested  in  the 
intestine  even  more  vigorously  than  in  the  stomach.  But 
stomach  digestion  is  a  very  important  factor,  for  while  the 
proteids  themselves  can  be  acted  on  in  the  intestine,  the 
connective  tissue  that  holds  the  muscle  fibres  together,  will 
be  less  quickly  dissolved  there  because  of  the  absence  of  acid 
in  the  intestinal  secretions.  Without  the  influence  of  the 
gastric  juice  the  muscle  fibres  will  not  be  readily  set  loose 
so  that  the  juices  may  act  upon  them.  ''  Stomach  digestion" 
is  thus  an  important  preliminary  to  **  intestinal  digestion. '^ 

2.  Gastric  juice  produces  a  great  chemical  change  in  the 
proteids.  Strange  as  it  may  seem  at  first  sight,  these  very 
important  foods,  of  which  meats,  milk  and  eggs  are  typical 
examples,  cannot  be  taken  through  the  wall  of  the  intestine, 

ito  the  blood  or  be  of  any  use  to  us  unless  they  first  cease 


94  ADVANCED  PHYSIOLOGY 

to  be  proteids.  They  cannot  he  absorbed  as  proteid  even  though 
our  own  muscles  and  blood  are  largely  of  proteid  material. 
The  change  which  proteids  must  go  through  is  a  chemical 
•"one,  and  the  first  step  toward  it  is  brought  about  by  the 
hydrochloric  acid  and  the  pepsin  in  the  gastric  juice.  This 
pepsin  is  one  of  the  ferments,  or  enzymes,  to  which  attention 
was  directed  in  an  earlier  chapter,  and  under  its  influence  the 
proteids,  which  are  very  complex  bodies,  are  broken  into  simpler 
ones.  These  new  bodies,  peptones,  proteoses,  and  allied  sub- 
stances, are  no  longer  real  proteids  but  are  far  simpler  chem- 
ically, and  may  readily  pass  through  the  wall  of  the  stomach. 
It  is  probable,  however,  that  a  large  part  of  the  proteid  eaten 
is  carried  on  into  the  intestine  and  still  further  modified 
before  absorption. 

Milk  cbntains  much  proteid  in  the  form  of  casein.  This 
casein,  however,  is  not  readily  acted  on  by  pepsin  until  the 
milk  is  curdled.  Rennin,  the  second  enzyme  in  gastric  juice, 
produces  the  curdling  action  on  milk.  It  is  from  a  similar 
curd  that  cheese  is  made,  cheese-makers  adding  to  their 
milk  rennet  which  is  usually  obtained  by  a  process  of  extrac- 
tion and  refinement  from  the  stomachs  of  calves.  Calves' 
diet  consists  mainly  of  milk  and  their  gastric  glands  contain 
great  quantities  of  rennin. 

From  these  facts  it  is  evident  that  milk  taken  into  the 
stomach  is  speedily  soured  by  the  acid  in  the  gastric  juice 
and  curdled  by  the  rennin.  If  a  baby  vomits,  and  its  milk 
is  found  to  be  curdled  and  sour  it  may  indicate  that  the  child 
has  eaten  more  than  it  can  comfortably  hold  in  its  stomach, 
but  the  changes  in  its  food  only  show  that  digestion  is  going 
on  properly. 

On  sugars  and  starches  gastric  enzymes  have  practically  no 
effect.  Indeed,  the  digestion  of  starches  which  was  begun 
by  the  saliva  in  the  mouth  stops  after  the  food  has  become 
mixed  with  the  gastric  juice,  because  the  salivary  enzymes  will 
not  act  in  an  acid  solution,  and  there  is  considerable  acid  in 


DIGESTION  OF  FOOD:     THE  (ESOPHAGUS 


95 


Brain 


the  gastric  juice.  It  takes  some  time,  however,  for  the 
swallowed  food  to  become  thoroughly  mixed  with  the 
gastric  juice  and  therefore,  for  perhaps  an  hour  after 
reaching  the  stomach,  the  conversion  of  starch  into  sugar 
continues. 

For  a  long  time  it  was  held  that  fat  undergoes  only  melt- 
ing and  emulsification  in  the  stomach;  but  more  recent 
studies  show  the  presence,  in  a  Hmited  way,  of  a  third  fer- 
ment, gastro-lipase,  which  changes  fats  into  glycerin  and 
fatty  acids.  Absorption  of  fats  is  now  possible,  but  prob- 
ably this  does  not  occur  till  they  have  gone  on  into  the  in- 
testinal division  of  the 
alimentary  canal. 

The  Flow  of  the  Gastric 
Juice ;  —  Between  meals, 
when  the  stomach  is 
practically  empty,  its 
walls  are  of  a  pale  pink 
color,  and  the  lining  is 
merely  moist;  very  httle 
secreting  work  is  done  by 
the  glands.  But,  on  the 
entrance  of  food,  the 
blood  vessels  in  the 
stomach  walls  expand, 
and  more  blood  flows 
around  the  glands,  the 
cells  of  which  begin  a 
copious  secretion.  Like 
the  case  of  the  salivary 
secretions,  this  response 
of  the  blood  vessels  and 
glands  is   a   reflex   action, 


Spinal 
■Cord 


Fig.  51. — Diagram 

Showing  the  method  by  which  the  stomach 
receives  its  nerves  from  the  brain  and  cord. 
The  nerves  from  the  cord  actually  come 
through  the  sympathetic  system,  not  shown 
in  the  figure.       (Modified  from  Openchowski; 

controlled    by  the   central   ner- 


vous system.     The  actual  contact  of  the  mouth  or  stomach 


96  ADVANCED  PHYSIOLOGY 

with  food  is  not  necessary  since  the  mere  sight  or  smell  of 
food  is  all  that  is  required  to  produce  the  result.  The  stom- 
ach does  not  regulate  itself;  it  acts  only  at  the  command  of 
the  brain;   Fig.  51. 

It  is  necessary,  however,  that  the  person  be  conscious, 
or  secretion  will  not  occur.  If  food  is  put  into  the  stomach 
of  a  sleeping  dog,  no  gastric  secretion,  and,  therefore,  no 
digestion  occurs.  Again,  more  is  secreted  when  one'is  hungry 
than  when  one  swallows  food  though  not  hungry.  Pleasani 
tasting  foods  stimulate  more  active  secretion  than  unpleasant,] 
and  thus  we  can  conclude  that  pleasing  flavors,  althougl 
they  may  have  no  food  value,  may  have  a  decided  use  as 
aids  in  digestion. 

Sometimes  when  a  person's  digestion  is  poor,  so-callec 
predigested  foods  are  taken.  These  are  generally  protei( 
substances  which  have  been  treated  artificially  with  pepsii 
obtained  from  the  stomachs  of  pigs.  This  predigested  foo( 
can  be  handled  by  the  stomach  more  easily  than  ordinan 
food;  but  its  use  should  not  become  a  habit,  for  constantly 
aided  in  this  way  the  stomach  and  other  organs  become 
dependent  on  this  assistance  and  lose  their  natural  powers. 

Cold,  as  a  rule,  retards  the  action  of  any  gland,  muscle 
or  other  tissue  in  the  body,  while  heat,  within  limits,  is 
favorable  to  their  action.  In  the  stomach  the  glands,  togethei 
with  the  nerves  which  control  them,  are  so  near  the  surface 
that  large  quantities  of  cold  food,  like  ice  cream  or  ice  watery 
produce  a  shock  which  always  delays  their  normal  actioi 
The  distinct  pain  caused  by  too  warm  food  or  drink  prevents 
us  from  harming  ourselves  in  this  way.  It  is  interesting 
to  note  in  this  connection  that  heat  as  such,  is  not  feli 
when  food  is  swallowed;  the  sensation  is  one  of  pain  only. 

The  Passage  of  Food  into  the  Intestine. — The  length  of  time 
that  food  remains  in  the  stomach  varies  with  the  kind  of  foodj 
but  in  the  course  of  two  to  four  hours  after  the  average  mealj 
all  foods  have  become  a  finely  divided,  sUmy  mass  callec 


DIGESTION  OF  FOOD:  THE  (ESOPHAGUS  97 

chyme.  In  this  mass  after  an  ordinary  meal,  there  should  be 
water,  saliva,  mucus,  gastric  juice,  peptones,  unchanged 
proteid,  dissolved  sugars,  unmodified  starches,  curdled  milk, 
fat  droplets,  shreds  of  connective  tissue  and  vegetable  cellulose, 
the  woody  substance  in  plant  structures.  Responding  to  the 
presence  of  this  chyme,  the  muscles  in  the  pyloric  valve 
relax  and  allow  the  food  to  pass  on  into  the  small  intestine. 

The  mere  presence  of  chyme  in  the  stomach  does  not  pro- 
voke the  pyloric  valve  to  open  and  let  it  pass  through.  This 
would  obviously  be  poor  management  should  it  happen 
that  the  duodenum  were  already  full,  and  completely  busy 
th  its  work  on  chyme  previously  received.  It  will  be  re- 
embered  that  chyme  is  acid,  as  a  result  of  hydrochloric 
acid  in  the  gastric  juice.  In  contrast,  the  juices  of  the  intestine 
are  alkaline;  but  it  takes  some  time  for  the  intestinal  secre- 
tions to  overcome  the  acidity  of  material  received  from  the 
stomach.  When  this  acidity  is  finally  neutralized,  however, 
a  message  is  sent  from  the  intestine  to  the  pylorus  that  all 
is  in  readiness  for  a  further  installment  of  chyme  from  the 
stomach,  and  the  valve  opens.  Very  unexpectedly  this 
message  is  sent,  not  through  nerve  fibres  as  most  stimuli 
are,  but  through  the  blood  stream;  this  is  a  round-about 
method,  but  it  is  the  one  used  in  this  instance. 


vjwi 


CHAPTER   VII 
DIGESTION  OF  FOOD:  THE  INTESTINE 


Fig.    52. — The    digestive    organs    in 
the  abdomen 

The  stomach  and  liver  are  separated  for 
clearness'  sake.  They  are  really  in  close 
contact. 

A,  appendix;  B,  large  intestine;  C,  duodentim; 
D,  bile  duct;  E,  liver;  F,  gall  bladder;  G,  cys- 
tic duct;  H,  hepatic  duct;  /,  pancreas;  J,  sig- 
moid flexure;  K,  rectum;  L,  anal  aperture. 

98 


Many  people  have  a 
mistaken  idea  that  the 
stomach  is  the  all-impor- 
tant section  of  the  food 
canal,  the  chief  organ  of 
digestion,  and  that  almost 
as  soon  as  food  is  swal- 
lowed it  becomes  trans- 
formed by  some  marvel- 
lous influence  into  energy, 
heat,  muscle  or  brain. 
We  frequently  hear  a 
man  say  that  he  needs  a 
hearty  dinner  because  he 
is  to  work  hard  in  the 
afternoon,  thus  wrongly 
assuming  that  the  dinner 
of  the  day  furnishes  him 
with  immediate  muscular 
power.  But  little  if  any 
food  is  absorbed  from  the 
mouth  or  gullet,  and  little 
from  the  stomach.  Food 
is  of  no  value  until  it  has 
left  the  stomach  and,  not 
for  many  hours  after  eat- 
ing does  any  portion  of  it 
become  a  part  of  the  bodv 
itself.  The  power  to  do 
each  day's  work  comes 
from  the  food  eaten  the 
day    before   or,   perhaps, 


DIGESTION  OF  FOOD:  THE  INTESTINE 


99 


several  days  before.  Food,  after  leaving  the  stomach,  must 
still  pass  through  a  long  series  of  changes  before  it  is  of  any 
practical  value. 

The  intestine  may  be  considered  in  two  sections:  the  small 
intestine  and  the  large.  The  former  is  about  twenty  feet  in 
length,  and  the  latter  about  five;  the  total  length  below  the 
stomach  affords,  therefore,  a  large  amount  of  surface  for 
absorption;   Fig.  52. 

THE  SMALL  INTESTINE  AND  ORGANS  CONNECTED  WITH  IT 

The  small  intestine  commences  at  the  pyloric  valve  of  the 
stomach  and  extends,  coiling  much  on  the  way,  to  a  point  in 
the  right,  lower  part  of  the  abdominal  cavity,  where  it  enters 
the  large  intestine.  Its  average  diameter  is  about  one  inch. 
It   occupies    practi- 

yf  j  mTftoratKDual 


Ladiul 


LtfrnphOhnd 


cally  all  the  space 
in  the  lower  half  of 
the  abdominal  cav- 
ity, save  that  taken 
by  the  large  intes- 
tine, the  kidneys, 
bladder  and  spleen. 
Throughout  its 
length  it  is  loosely 
attached  to  the  dor- 
sal wall  of  the  cav- 
ity by  a  thin  sheet 
of  tissue,  the  mesen- 
tery. This  mesentery 
is  traversed  by  a 
multitude  of  arteries 
and  veins  on  their 
way  to  and  from  the  digestive  tract;  for  it  is  solely  through 
these  vessels  that  food  is  tak^n  iip;frpm  tbo^focd  p^i\^l  ^V^^ 
carried  over  the  body;  Fig^^^3/-;;   V     '^.^' T     *^,^/'\  :,,  ;■; 


Fig.  53. — Diagram 

Showing  a  piece  of  the  intestine  held  in  the  meb^n- 

tery  and  the  blood  and  lymph  vessels  in  it. 

The  mesenterj'  is  represented  as  narrower  than  it  actr 

ually  is  and  hence  the  lymph  glands  as  closer  to  the 

intestine. 


100  ADVANCED  PHYSIOLOGY 

After  the  food  has  been  in  the  stomach  for  an  hour  and  a 
half  or  two  hours,  the  valve  which  has  kept  it  from  going 
into  the  intestine  opens  and  allows  a  Uttle  of  it  to  pass  out, 
closing  again  quickly.  Soon  it  opens  again  and  more  of  the 
digested  food  passes  out,  for  this  valve  operates  like  a  very- 
sensitive  mechanism  which  allows  softened,  partly  dissolved 
food  to  pass  it,  but  closes  at  once  if  any  solid,  undigested 
food  touches  it.  The  food  thus  passes  out  of  the  stomach, 
a  little  at  a  time  into  this  long  tunnel,  where  it  is  to  be  still 
further  dissolved  and  changed  for  absorption.  Through  this 
tube  the  food  is  slowly  pushed  along  by  peristaltic  action  of 
muscles  in  its  walls,  similar  to  those  in  the  oesophagus. 
Almost  at  once  after  leaving  the  stomach  the  intestine  makes 
a  bend  downward  and  to  the  left,  thus  crossing  the  abdomen 
below  the  stomach  as  the  duodenum;  Fig.  52.  As  the  food 
mass  is  carried  around  this  bend  it  is  mixed  with  a  secretion 
which  enters  the  intestine  by  a  duct  shown  in  Figure  48,  and 
which  comes  from  two  large  and  very  important  organs,  the 
liver  and  the  pancreas. 

In  many  backboned  animals  these  two  organs  connect  with 
the  intestine  through  separate  ducts,  while  in  others  their 
ducts  join  as  in  man.  The  spleen,  which  is  near  by,  has  no 
connection  with  the  intestine  physiologically. 

The  Liver  and  its  Functions. — The  liver  is  a  large  gland, 
weighing  in  a  person  of  average  size  about  three  pounds, 
and  located  just  below  the  diaphragm. 

It  is  partially  divided  into  a  number  of  lobes.  There  is  a 
large  right,  a  smaller  left  lobe,  and  other  smaller  divisions, 
which  easily  adjust  themselves  to  the  neighboring  organs. 
The  stomach  over  which  its  lobes  hang  is  very  active;  the 
body  walls  are  constantly  moving,  and  the  diaphragm  pulls  the 
organs  up  and  down  as  one  breathes.  To  all  this  environment, 
the  liver  adjusts  itself,  its  lobes  gliding  easily  over  one  another, 
^3  well  as  oVer  tlie-  OrgAns  with  which  they  come  in  contact. 

'Everyone  IS  familiar  wiill  the  dark  red  appearance  of  the 


DIGESTION  OF  FOOD:  THE  INTESTINE  101 

l:>eef' s  liver  as  it  hangs  in  the  markets.  This  red  color  is  partly 
due  to  the  fact  that  the  organ  is  very  full  of  blood;  it  has  been 
estimated  that  one-quarter  of  all  the  blood  of  the  body  may 
be  in  the  liver.  Its  surface  shows 
a  mottled  appearance,  due  to  the 
arrangement  of  tissues  in  the  organ, 
for  it  is  really  a  large  compound 
gland;  Fig.  54. 

Beneath  the  right  lobe  is  the 
gall  bladder,  a  pear-shaped  sac, 
about  four  inches  in  length,  and 
at  its  widest  place  an  inch  in 
diameter.  Its  function  is  that  of  ^ig.  54.— The  surface  ot 
a  storage  reservoir  for  holding  the  ^^^  liver 

-  .,  X    J  1,      xu     T  1,         'J.  '  Slightly  magnified 

Dile  secreted  by  the  liver  when  it  is 

not  needed  in  the  intestine.  From  an  examination  of  Figure 
52,  it  will  be  seen  that  the  bile  does  not  run  directly  from  the 
liver  into  this  sac,  but  that  the  only  duct  leading  away  from 
the  organ,  the  hepatic,  goes  in  a  fairly  direct  line  to  the  first 
loop  of  the  intestine.  A  side  branch  from  this,  the  cystic 
duct,  leads  to  the  gall  bladder;  from  their  junction  to  the 
intestine,  is  a  tube  called  the  common  bile  duct. 

The  liver  keeps  steadily  secreting  but  the  demand  for  bile 
is  not  constant,  as  food  conditions  in  the  intestine  are  not 
always  the  same.  When  bile  is  not  needed  in  the  intestine 
the  common  bile  duct  closes,  and  the  bile,  then  coming  from 
the  liver,  goes  back  and  is  stored  in  the  gall  bladder  (Fig.  48); 
there  it  accumulates  until  the  opening  into  the  intestine 
again  allows  a  free  flow.  The  presence  of  chyme  coming  from 
the  stomach  causes  such  an  opening. 

The  large  size  of  the  liver  and  its  abundant  blood  supply 
suggest  that  the  organ  must  have  very  important  uses.  The 
amount  of  fluid  which  it  secretes  daily  varies  in  different  per- 
sons from  a  pint  to  a  pint  and  a  half;  it  is  a  little  thicker  than 
water,  and  of  a  golden  brown  color.    Notwithstanding  this 


102 


ADVANCED   PHYSIOLOGY. 


abundant  secretion,  which  amounts  to  about  one  and  one- 
half  pints  per  day  in  an  adult,  it  is  surprising  to  learn  that 
until  recently  little  was  known  as  to  the  value  of  bile  as  it 
mixes  with  food  materials  in  the  intestine. 

At  least  three  uses  for  it  are  now  recognized;  of  these  the 
most  important  is  that  it  intensifies  the  action  of  pancreatic 
juices  about  three-fold.  Another  function  is  the  dissolving  of 
fatty  acids  and  making  them  more  absorbable;  when  its  flow 
is  prevented,  not  only  is  fat  only  partially  digested  and 
unabsorbed,  but  a  fatty  coating  adheres  to  other  kinds  of 
food  and  prevents  digestive  jui  es  having  access  to  them,  thus 
letting  them  pass  from  the  body  unused.  Bile  also  prevents 
rapid  growth  of  bacteria  in  the  intestine  with  consequent 
putrefaction  and  gas  formation,  though  by  itself  it  deteriorates 
easily. 

Other  important  functions  of  the  liver  will  be  pointed  out 
in  their  proper  connections  later. 

The  Pancreas  and  its  Functions. — Unlike 
bile,  the  fluid  secreted  by  the  pancreas 
plays  a  necessary  part  in  the  digestive 
process.  As  can  be  seen  from  Figure  48,  a 
duct  from  the  pancreas  joins  the  common 
bile  duct  just  before  the  latter  enters  the 
intestine. 

The  pancreas  is  what  the  butcher  calls 
the  "sweetbread."  In  the  human  being 
it  is  about  seven  inches  long  by  one  and  a 
half  broad,  and  one-half  inch  thick;  not 
a  very  large  organ  but  of  great  impor- 
tance. It  is  spongy  in  texture,  and  lies, 
attached  loosely,  along  the  lower  curved 
border  of  the  stomach.  Its  structure,  as 
shown  in  Figure  55,  is  very  Uke  that  of  the  salivary  glands. 
The  liquid  output  of  its  cells  amounts  to  about  one  and  one- 
half  pints  a  day,  and  is  clear  and  watery  in  appearance.     Zz 


Fig.  55. — A  highly 

MAGNIFIED  VIEW 
OP  A  BIT  OF  THE 
PANCREAS  SHOW- 
ING   ALVEOLI 

(Maziarski) 


DIGESTION  OF  FOOD:     THE  INTESTINES  103 

contrast  to  the  acid  secretions  of  the  gastric  glands,  the 
pancreatic  secretion  is  strongly  alkaline. 

Food  as  it  leaves  the  stomach  is  by  no  means  completely- 
digested.  The  starch  is  only  partially  changed  to  sugar;  much 
of  the  proteid  passes  through  the  stomach  without  change, 
and  the  fats,  though  melted  and  emulsified  in  part,  have  been 
only  partially  digested,  if  at  all. 

The  fluid  derived  from  the  pancreas  has  the  power  to  dis- 
solve and  change  any  kind  of  food,  this  being  accomphshed  f or 
the  most  part  by  three  different  ferments  (enzymes),  as  follows: 

1.  Trypsin,  which  starts  the  digestion  of  proteids  by 
changing  many  of  them  to  peptones,  thus  supplementing  the 
work  of  the  gastric  juice. 

2.  Amyolopsin,  which  converts  starches  into  sugars,  thus 
completing  the  action  of  the  saliva. 

3.  Lipase  (steapsin),  under  the  action  of  which  fats  are 
split  up  and  made  absorbable,  i.  e.  digested. 

The  influence  of  trypsin  is  similar  to  that  of  pepsin  although 
more  complete;  it  also  acts  upon  the  proteids  which  have 
been  partly  changed  into  peptones,  and  breaks  them  up  still 
further  chemically;  this  action  continues  till  all  proteid  mat- 
erial has  been  reduced  to  very  simple  substances  called  amino- 
acids.  These  differ  from  proteids  in  that  they  are  composed 
of  much  smaller  molecules,  are  soluble  in  water,  do  not 
coagulate  with  heat,  and  easily  pass  through  membranes. 
Probably  most,  if  not  all,  the  peptones  are  changed  into  amino- 
acids  before  absorption,  this  final  step  being  brought  about 
by  a  ferment,  erepsin,  secreted  by  the  intestinal  wall  glands. 

About  eighteen  different  amino-acids  are  now  recognized  as 
resulting  from  the  complete  digestion  of  different  sorts  of  pro- 
teid foods.  Some  of  these,  e.  g.  arginine  and  glutaminic  acid, 
are  abundant,  i.  e.  derived  from  many  proteid  sources;  others, 
e.g.  cystine,  are  seldom  formed  ;tryotophane  (derived  from  milk 
and  wheat)  and  lysine  (from  milk  and  eggs)  are  very  essential 
to  growth,,  while  glutaminic  acid  (from  milk,  eggs,  wheat,  peas. 


104  ADVANCED  PHYSIOLOGY 

etc.)  is  a  proteid  product  with  very  limited  food  value. 

We  thus  see  that  there  is  a  genuine  basis  for  the  arguments 
which  insist  on  a  varied  diet;  for  not  all  the  substances  in  even 
the  so-called  "best  foods'*  have  real  nutritional  value. 

The  amylopsin  acts  upon  starches  much  as  does  the  ptyalin 
of  saliva  and  completes  their  change  into  sugar. 

The  steapsin  acts  upon  the  fats  causing  their  digestion. 

Two  very  different  changes  take  place  in  ^ 

them.     First,  much  of  the  fat  is  broken  up  in-       c<§ip%Oo  o 
to  extremely  minute  droplets,  which  float  in     '^o°o^^pO(5Co 
the  hquid  of  the  food.     In  this  condition  it  re-  ^^2o^o^6 
sembles  the  fat  of  milk  and,  indeed,  the  entire     ^oo^°q^^S°^^ 
contents  of  the  intestine,  because  of  this  con-  °  o^°qO 

dition  of  the  fat,  become  more  or  less  white  Fig-   56. — Emulsi- 
like  milk.     Such  a  condition  of  finely  divided  ^^^^  ^■^'^ 

fat  droplets  is  called  an  emulsion;  Fig.  56.  'Tghiy  iTagnmet'^' 
It  was  formerly  thought  that  these  fat  drop- 
lets were  absorbed  directly  through  the  walls  of  the  intestine 
into  the  blood ;  but  it  is  now  known  that  a  second  change  takes 
place  in  part  of  the  fat,  if  not  in  all,  before  it  is  really  absorbed. 

This  is  a  chemical  change  which  results  in  splitting  up  the 
fat  molecules  into  two  different  substances  called  fatty  acids 
and  glycerine  —  both  of  which  are  easily  absorbed.  Their 
reformation  into  fat  occurs  very  promptly,  however,  for  true 
fat  droplets  are  found  abundantly  in  the  lining  cells  of  the 
intestine,  immediately  after  fat  digestion.     See  Fig.  64. 

No  digestive  gland  has  such  varied  and  efficient  powers  as 
the  pancreas.  The  pancreatic  fluid  digests  any  food  that  has  not 
been  acted  on  by  the  other  digestive  juices.  Some  foods,  espe- 
cially complex  sugars,  may  be  simplified  by  enzymes,  e.  g. 
maltose  (which  acts  on  starch-sugars)  and  lactose  (which 
ni odifies  milk-sugar)  occurring  in  juices  which  are  added  to 
the  food  mass  by  cells  in  the  intestinal  lining. 

After  the  food  is  completely  digested,  it  is  wholly  changed 
in  nature  and  appearance.  It  was  swallowed  as  meat,  pota- 
toes, bread  and  butter  or  milk;  it  has  become  dissolved  into  a 


DIGESTION  OF  FOOD:  THE  INTESTINE 


105 


Villi. 


GtandfoC, 
Liebetkuhh 


whitish,  syrupy  liquid,  called  chyle,  in  which  there  are  but 
few  remnants  of  solid  material.  Its  proteids  have  become 
peptones  or  even  simpler  bodies;  its  starches  are  all  sugars; 
and  its  fats  are  either  emulsified  or  are  changed  into  fatty 
acids  and  glycerine.  It  is  not  until  the  food  has  flowed 
through  a  considerable  section  of  the 
intestine  that  digestion  is  complete. 

The  walls  of  the  small  intestine, 
shown  in  Figure  57,  are  composed 
of  muscles  that  force  the  food  along, 
of  glands,  the  secretion  of  which  re- 
sembles that  of  the  pancreas,  and  of 
viUi  (described  in  the  next  chapter). 

THE  LARGE  INTESTINE 

The  small  intestine  empties  into 
the  large  intestine  in  the  lower  right 
side  of  the  abdominal  cavity.  The 
opening  from  one  to  the  other  is  little 
more  than  a  slit,  the  sides  of  which 
open  easily  in  one  direction  but  not 
in  the  other;  Fig.  58.  Hence  food 
passes  readily  onward,  but  not  back- 
ward. The  part  of  the  large  intestine 
thus  entered  is  the  colon,  and  the 
general  shape  of  the  course  which 
it  takes  is  that  of  an  inverted  letter 
U;  i.  e.  beginning  on  the  lower  right  side  of  the  body  cavity 
I      it  passes  up  that  side  as  far  as  the  liver  (ascending  colon); 

Iien  it  crosses  to  the  left  side  of  the  body  (transverse  colon), 
ad  there  passes  downward  (descending  colon);   Fig.  52. 
The  small  intestine  opens  into  the  side  of  the  large  intes- 
ne  (see  Figs.  52  and  58);  about  two  and  a  half  inches  of 
I      the  latter  are  thus  left  below  the  opening  as  a  short  section 
ending  blindly  and  called  the  coecum,  a  word  meaning  "  blind." 


Circulort- 
tluscles 


ilonfitudinhr^ 

tiusclej 
Fig.  57. — A  cross  section 

THROUGH   THE   WALL  OP 
THE  SMALL  INTESTINE 
(Modified  from  Oppel). 


106 


ADVANCED  PHYSIOLOGY 


Coecum 


tnfesfim 


orm 


From  the  lower  end  of  the  ccecum  protrudes  a  short  hollow 
tube  called  the  vermiform  appendix;  this  varies  in  size  in 
different  people  but  it  is  usually  from 
three  to  six  inches  long,  and  a  quarter 
of  an  inch  or  more  in  diameter.  The 
cavity  opens  into  the  coecum. 

Beyond  the  lower  end  of  the  descend- 
ing colon  the  intestine  passes  into  an 
S-shaped  portion  called  the  sigmoid 
flexure;  from  this  all  intestinal  contents 
enter  the  final  section  of  the  digestive 
tract,  the  rectum.  This  opens  to  the 
exterior  by  the  anal  aperture;  Fig.  52. 
The  walls  of  the  large  intestine  are 
constructed  practically  like  those  of  the 
small;  but  there  seem  to  be  no  glands 
opening  into  it  which  are  concerned 
with  the  digestion  of  food,  though 
mucous  glands  are  numerous.  The  food  may  not  be  wholly 
digested  in  the  small  intestine  and  so  digestive  processes, 
to  a  small  extent,  go  on  here  although  not  by  virtue  of 
the  glands  of  the  large  intestine  itself.  There  is  also  very 
rapid  absorption  from  this  region,  particularly  of  water,  and 
this  causes  the  intestinal  contents  to  become  more  and  more 
hard.  Much  of  this  "  undissolved  food  "  performs  a  valuable 
service,  however,  by  mechanically  stimulating  the  walls  of 
the  intestine  and  thus  causing  more  rapid  peristaltic  action. 
A  more  certain  passing  along  of  food  materials  is  thus  ensured 
and  so  the  trouble  called  constipation  is,  in  a  measure,  pre- 
vented. If  only  very  fine  foods,  e.  g.  those  made  from 
finely  powdered  flours,  are  eaten,  the  water  in  them  may  be 
absorbed  quickly  and  then  the  mass  becomes  so  dry  and 
unyielding  that  it  is  forced  along  the  canal  with  great  diffi- 
culty. Coarse  foods,  which  are  sometimes  refused  by  persons 
who  proudly  consider  thern  too  crude  ^nd  cheap  for  their 


Verrnii 
AppendtK 

Fig.  58. — The  begin- 
mng  of  the  large 
intestine 

Showing  the  opening 
from  the  small  intestine 
at  some  distance  from 
its  end. 


DIGESTIOJVJ   OF  FOOD:  THE  INTESTINE  107 

refined  taste,  are  often  not  only  very  nutritious,  but  as  a  rule  nec- 
essary for  uniformly  good  digestion  and  therefore  good  health. 
Those  materials  which  are  not  changed  into  a  liquid  condition 
are  never  absorbed  and  never  become  parts  of  the  body. 

After  the  nutritive  part  of  the  intestinal  contents  has  been 
absorbed  there  remains  a  considerable  portion  of  undigested 
matter  which  is  now  useless  and  is  passed  to  the  exterior 
as  faeces.  The  elimination  of  these  wastes  once  a  day  is  of  al- 
most as  much  importance  to  health  as  the  regular  taking  of 
food.  The  intestinal  contents  after  food  absorption  readily 
undergo  putrefaction  from  the  growth  of  bacteria  and  soon 
become  filled  with  poisonous  substances  which  injure  the 
body  materially  if  the  wastes  are  not  regularly  removed. 
Their  retention  is  apt  to  result  in  headaches  or  other  bodily 
derangements.  Disturbances  by  which  the  wastes  are  re- 
tained too  long  (constipation)  or  by  which  they  are  discharged 
too  frequently  and  in  too  liquid  condition  (diarrhea)  are  both 
to  be  avoided.  Such  conditions  are  due  as  a  rule  to  an  error 
in  methods  of  living.  One  may  be  eating  improper  food; 
he  may  be  eating  too  much  food  or  too  often;  he  may  be  eating 
too  much  fine  food  like  wheat  flour  and  not  enough  coarse 
food  or  he  may  not  be  drinking  enough  water.  He  may 
be  living  a  too  sedentary  life;  constipation  especially  is  fre- 
quently due  to  insufficient  exercise  and  may  be  remedied  by 
various  forms  of  bodily  activity.  The  improper  method  of. 
fighting  these  troubles  is  to  use  medicine ;  for  drugs  only  palUate 
•  and  do  not  cure  them.  Regularity  in  expelling  the  waste  large- 
ly depends  upon  hahit.  A  little  care  and  attention  will  enable 
almost  any  one  to  acquire  regular  habits  that  will  be  of  lasting 
value  to  his  general  health.  No  one  whose  intestine  is  crowd- 
ed with  poisoning  wastes  can  continue  in  good  health. 


I 


DIGESTION  OF  DIFFERENT  FOODS 


Since  no  food  can  be  absorbed  into  the  body  until  it  is 
gested,  the  readiness  with  which  a  food  can  be  digested  is  a 


106  ADVANCED  PHYSIOLOGY 

factor  in  determining  its  value.  Cheese  is  the  most  nutritious 
of  our  foods,  but  it  is  such  a  condensed  food  that  only  a  little 
of  it  should  be  eaten  at  one  time.  Peas  and  beans  are  also 
very  nutritious  foods,  containing  a  large  amount  of  proteid; 
but  these  again  are  too  difficult  of  digestion  to  be  used 
like  bread,  as  a  constant  article  of  diet.  The  digestive 
tract,  however,  can  perfectly  well  handle  a  considerable  amount 
of  foods  that  are  difficult  to  digest  and  it  is  better  to  use  some 
of  them  rather  than  to  give  the  digestive  organs  too  easy  a 
task.  But  in  choosing  one's  diet,  it  is  well  to  bear  in  mind 
that  foods  like  milk,  bread,  rice,  soft  boiled  beef,  mutton  and 
broiled  meats  are  more  easily  utilized  than  are  beans,  peas, 
nuts,  hard  boiled  eggs,  pork,  veal,  fried  foods  and  cheese. 

ALCOHOL  AND  INDIGESTION 

Various  opinions  have  been  held  as  to  the  effect  of  alcohol 
on  digestion.  That  it  produces  serious  troubles  whea  used  in 
large  amounts  is  questioned  by  no  one,  but  it  has  been  a  popular 
belief  that  when  used  in  small  quantities  it  aids  digestion. 
The  most  careful  testing  of  this  theory  has  shown  that  it  is 
a  mistake.  Alcohol  has  two  opposite  effects  upon  digestion. 
It  causes  increased  secretion  of  some  of  the  digestive  juices, 
chiefly  the  saliva  and  gastric  juice.  To  this  extent  it  might 
be  supposed  to  promote  digestion.  But,  on  the  other  hand,  its 
presence  in  the  stomach  tends  to  weaken  the  action  of  the 
digestive  ferments  and  this  serves  to  counteract  the  apparent 
advantage  of  the  increased  secretion.  As  a  result,  when  used 
in  small  quantities  alcohol  neither  hastens  nor  retards  diges- 
tion; when  used  in  larger  amounts,  its  retarding  action  is  al- 
ways certain. 

With  certain  alcoholic  drinks,  the  retarding  action  is 
especially  evident  and,  oddly  enough,  this  is  true  of  many 
wines  that  are  not  infrequently  taken  as  '^  appetizers  "  with 
meals,  under  the  false  impression  that  they  facilitate  digestion. 
Experiments  with  these  wines  show  that  they  have  a  very 


DIGESTION  OF  FOOD:  THE  INTESTINE  109 

Itsonsiderable  checking  action  upon  digestion,  greater  than 
■hat  of  pure  alcohol.  The  effect  is  due  in  these  cases  to  other 
lubstances  in  the  wines  as  well  as  to  the  alcohol. 
I  In  short,  it  is  an  established  fact  that  alcoholic  drinks  are, 
m  least  to  healthy  persons,  of  no  use  in  digestion  and  rarely 
ft  ever  of  value  in  illness.  On  the  contrary  they  are  usually, 
and  perhaps  always,  a  direct  detriment.  It  is  not  strange, 
however,  that  persons  who  have  used  wine  for  a  long  time 
think  that  it  aids  digestion  since  they  have  by  its  use  brought 
their  bodies  into  a  condition  in  which  the  digestive  glands 
will  not  act  normally  without  it. 

DISEASES  OF  THE  INTESTINAL  TRACT 

Summer  Complaint. — Very  often  something  one  has  eaten 
produces  a  quick  and  rather  violent  disturbance  of  the 
digestive  organs;  a  feeling  of  nausea,  followed  by  vomiting, 
frequently  by  pain  in  the  stomach  and  bowels,  occurs,  and 
perhaps  also  diarrhea.  The  cause  is  often  hard  to  determine 
exactly,  but  the  trouble  is  practically  always  due  to  improper 
food  or  drink.  It  is  conamon  in  hot  weather  and  therefore 
has  been  called  summer  complaint  While  sometimes  violent, 
it  is  usually  not  serious,  and  under  ordinary  conditions  will 
pass  away  in  a  day  or  two  if  the  person  remains  comparatively 
quiet  and  is  careful  as  to  what  he  eats. 

Peritonitis.^— We  have  noted  that  the  abdominal  cavity  is 
lined  with  a  very  delicate  membrane  in  a  fold  of  which  the 
intestine  is  held.  These  tissues  sometimes  become  inflamed, 
the  many  blood  vessels  in  them  becoming  distended.  At  the 
same  time  the  sensitiveness  of  the  parts  becomes  very  great, 
and  much  pain  is  felt  in  the  abdomen.  The  condition  is  known 
as  peritonitis,  a  word  derived  from  peritoneum,  the  name 
of  the  abdominal  lining.  Peritonitis  may  be  very  serious  and 
even  fatal;  for  in  its  severe  form  the  blood  vessels  may  burst, 
causing  exudation  into  the  abdomen  and  other  serious  com- 
plications.    It  is  characterized  by  continued  pain  in  the  ab^ 


110  ADVANCED  PHYSIOLOGY 

domen  which  must  not  be  confused  with  an  ordinary  stomach 
ache  due  to  improper  eating. 

Appendicitis. — We  have  already  noticed  the  vermiform 
appendix  (Fig.  52)  which  opens  into  the  large  intestine 
by  a  small  aperture.  It  occasionally  happens  that  an  in- 
flammation starts  in  the  appendix;  it  becomes  swollen,  and 
its  blood  vessels  expand,  causing  pain  and  soreness  on  the 
right  side  of  the  abdomen,  which  shows  the  presence  of 
appendicitis.  This  disease  is  a  very  serious  one;  for  if  pus 
accumulates  in  the  appendix  and  it  is  not  drained  off  through  the 
lumen  into  the  intestine,  the  appendix  is  likely  to  burst,  the 
pus  escaping  freely  into  the  abdominal  cavity.  When  this 
occurs  it  is  commonly  followed  by  general  peritonitis,  with  fatal 
results.  The  serious  nature  of  the  trouble  makes  it  advisable 
to  consult  a  physician  when  symptoms  such  as  above  described 
are  felt.  The  majority  of  cases  may  be  cured  by  the  removal 
of  the  appendix,  a  surgical  operation  which,  if 
performed  in  time,  involves  little  danger. 

The  real  inciting  causes  of  peritonitis  and  appen- 
dicitis are  not  yet  thoroughly  imderstood  and  at 
present  we  know  of  no  rules  for  avoiding  them. 
Fig.  59.— Ty-        Typhoid  Fever. —  Typhoid  fever  is  caused  by 
PHoiD    BA-    ij^Q  entrance  into  the  intestine  of  a  well  known 
^^^'^         ,    bacterium  (Fig.  59)  which  grows  abundantly  there 

The  cause  of  .  t  -   ^       re  i      i       i        • 

typhoid    fe-    and  excretes  poisons  which  affect  the  body  tissues. 

^®^-  There  are  certain  definite  symptoms  of  the  disease, 

one  of  which  is  a  fever  that  may  last  several  weeks.  Doctors  can 
do  little  to  cure  it  beyond  maintaining  the  strength  of  the 
body  so  that  the  person  may  have  the  power  to  drive  off  the 
trouble  himself.  It  is  one  of  the  most  serious  illnesses,  and  it 
causes  many  deaths  each  year.  About  10%  of  those  taking  the 
disease  die,  and  many  others  are  incapacitated  for  work  by 
it  for  weeks  or  months,  and  sometimes  permanently.  It  is 
more  common  in  th?  fall  than  at  any  other  season. 

The  sources  from  which  one  is  liable  to  obtain  typhoid 


DIGESTION  OF  FOOD :  THE  INTESTINE  111 

i)acteria  are  well  known.  Drinking  water,  if  in  any  way 
polluted  with  sewage,  is  almost  certain  to  contain  typhoid 
germs.  Hence,  water  from  brooks,  reservoirs,  rivers,  lakes 
or  wells  that  receive  any  sewage  is  unsafe  to  drink. 

Milk  is  also  a  source  of  typhoid  infection.  If  there  is  a 
case  of  typhoid  fever  at  a  farm  w^here  milk  is  produced,  the 
genus  are  pretty  sure  to  get  into  the  milk.  Oysters  which 
have  been  placed  near  the  mouth  of  a  river  for  the  sake  of 
^'floating"  them  are  also  occasionally  infected  with  the  bac- 
teria, and  if  eaten  uncooked,  cause  the  disease.  Flies  are  apt 
to  carry  the  germs  on  their  feet  and  deposit  them  on  the  food 
upon  which  they  feed. 

i  o  avoid  the  dangers  of  typhoid  fever  one  should  drink  none 
except  the  purest  water,  be  especially  careful  of  the  milk  sup- 
ply, and  not  allow  flies  to  alight  on  food  or  dining  tables.  Both 
water  and  milk  can  be  made  perfectly  safe  by  boiling. 

A  very  successful  method  of  avoiding  typhoid  fever  is  by  an 
inoculation  with  anti-typhoid  vaccine.  This  is  injected  uiider 
a  person's  skin  and  thus  renders  him  immune  against  typhoid 
fever  for  two  or  three  years.  It  is  very  widely  used  with 
soldiers,  and  it  is  wise  for  persons  who  are  to  travel,  where 
they  cannot  properly  control  their  food  and  water,  to  thus 
protect  themselves. 

Hookworm. —  This  disease  is  caused  by  a  small  parasitic 
worm.  A  person  becomes  infected  sometimes  by  taking  these 
worms  into  the  mouth  with  food  or  drink,  but  more  com- 
monly by  getting  dirt  containing  them  onto  the  hands  or  feet. 
They  usually  find  their  way  to  the  intestine  where  they  may 
live  for  a  long  time.  The  symptoms  of  the  disease  are  a  dry  or 
yellow  skin,  anaemia  (paleness),  stupid  facial  expression,  emacia- 
tion, irregularities  in  appetite  and  breathing,  weakness  in  the 
muscles,  headache,  defective  mentality,  and  some  others.  The 
disease  is  quite  easily  cured  by  treatment  with  thymol.  This 
disease  is  very  common  in  the  South,  especially  among  those  who 
go  barefoot,  since  they  are  very  easily  infected  through  their  feet. 


k 


CHAPTER  VIII 
THE  ABSORPTION  OF  FOODS 

It  is  very  natural  to  compare  the  body  to  a  factory  and  the 
alimentary  tract  to  the  furnace  room  where  fuel  is  being 
burned.  In  both  factory  and  furnace  there  is  motion,  work 
is  being  done  and  heat  is  being  produced. 

This  comparison  is  not,  however,  entirely  applicable.  In  a 
factory  the  fuel  is  burned  in  the  furnace,  only  the  heat  from 
the  flames  passing  through  the  furnace  walls.  In  our  bodies, 
on  the  contrary,  the  materials  themselves  in  the  digestive  tract 
pass  through  the  intestinal  walls  and  are  transported  around 
the  body.  No  heat  at  all  comes  from  the  digestive  tract,  for 
the  food  gives  up  none  of  its  stored-up  properties  until  it  has 
passed  out  of  this  tract  and  been  carried  to  its  final  destina- 
tion in  the  hands,  in  the  brain,  in  the  liver  or  elsewhere.  The 
intestine  is  therefore  not  properly  comparable  to  a  furnace 

A  better  analogy  would  be  to  compare  the  human  body  to  a 
city,  from  the  gas  plant  of  which  gas  is  sent  to  different  parts 
of  the  city;  some  of  it  is  to  be  used  for  cooking,  some  for 
lighting,  some  for  heating.  Some  of  the  heat  is,  perhaps, 
employed  for  producing  steam  pressure  in  an  engine,  which_ 
in  turn  runs  a  sewing  machine,  a  lathe  or  a  water  pump^ 
The  material  used  in  producing  the  heat  is  prepared  in  on( 
part  of  the  city,  but  it  gives  off  neither  heat  nor  power  noi 
light  there,  nor  while  going  through  the  pipes.  It  is  really 
used  only  after  it  has  reached  some  little  nook  or  corner,  ii 
attic  or  basement,  sleeping  room,  kitchen  or  shop;  there  11 
gives  out  its  light,  heat  or  power. 

STRUCTURES  CONCERNED  IN  ABSORPTION 

We  have  traced  the  food  to  the  intestine  and  noted  it  thei 
in  the  form  of  chyle,  ready  to  be  absorbed.     The  small  in- 

\12 


THE    ABSORPTION    OF    FOODS 


113 


Fig.  60. — Appearance  of  the 
interior  of  the  intestine 

Showing  the  folding  of  its  lining. 


oithelium 


testine  is  practically  a  tube  within  a  tube,  the  outer  of  which 
is  for  the  most  part  muscular.     If  we  imagine  the  inner  tube 
to  be  longer  than  the  outer,  the 
inner  tube  will  consequently  be 
thrown  into  ridges  which  go  trans- 
versely around  it,  intruding  on  the 
cavity  more  or  less.    Some  but  not 
all  of  the  ridges  will  pass  entirely 
around  the  tube;  Fig  60.     Further- 
more the  whole  lining,  ridges  and 
all,  is  covered  with  minute,  flex- 
ible   projections,    almost    as     if 
there  were  tiny  fingers  protruding 
mto  the  food  mass  of  the  intestine. 
These  fingers  are  called  villi,  and 
they  take  the  food  from  the  intestine  by  a  method  of  their 
own.     They  are  just  long  enough  to  be 
seen  with  the  naked  eye;   Fig.  61. 

Into  each  villus  extends  a  nerve   and 
also  a  tiny  branch  of  one  of  the  arteries 

walls.     This    arteriole 

the  end  of  the  villus 

up  into  much  smaller 
blood  vessels,  which  thus  form  a  sort  of 
network;  Fig.  62.  After  passing  through 
this  network  and  picking  up  food  in  a 
m  anner  to  be  described  presently,  the  blood 
returns  again  through  veins  to  the  intes- 
tinal wall  and  is  then  carried  off  once  more 
into  the  body.  Each  villus  contains 
another  tube  also  (Fig.  61),  called  a  lacteal, 
which  receives  the  fats  of  the  food.  A 
single  layer  of  cells,  the  epithelium,  covers 
each  villus  and  separates  the  blood  vessels 
and    lacteals   from    the    liquid    contents 


in    the    intestinal 
extends   nearly  to 
and    there   breaks 


l/fe/W 


^    _    Artery 


Fig.  61. — A  Single 
Villus 

Highly  magnified. 

of    the    intestine. 


114 


ADVANCED  PHYSIOLOGY 


OSMOSIS 


Clands 
of" 

Uebtrkm 


How  is  food  actually  absorbed  through  the  intestinal  walls? 
Two  liquids,  the  blood  and  the  dissolved  food,  are  separated 

by  a  thin  moistened  membrane. 
How  is  it  possible  for  the  liquid 
to  flow  in  one  direction  and  not  in 
the  other?  In  other  words,  why 
does  the  liquid  food  go  through 
into  the  blood  vessels,  and  the 
blood  at  the  same  time  not  pass 
out  into  the  intestine?  Physiol- 
ogists are  as  yet  able  to  give  only 
a  partial  answer  to  this  rather 
puzzling  question. 

Food  absorption  depends  partly 
upon  a  process  called  osmosis. 
In  the  first  place  it  is  not  quite 
true  that  food  passes  from  the 
intestine,  and  that  nothing  passes 
in  the  other  direction;  for  a  cer- 
tain amount  of  liquid  does  pass 
into  the  intestinal  canal  from 
the  blood.  But  the  latter  is 
small  in  amount,  perhaps  chiefly 
water,  and  more  material  passes 
in  the  reverse  direction.  To 
show  how  such  a  transfer  could 
take  place,  an  illustration  will  be 
useful.  Procure  a  piece  of  mem- 
branous tube,  like  that  used  for 
the  covering  of  sausages.  Fill 
this  with  a  solution  of  pure  grape  sugar  and  suspend  it  in 
a  jar  full  of  water,  as  shown  in  Figure  63.  The  tube  may 
thus  represent  the  intestine  full  of  digested  food,   and   the 


Muscles- 


Fig.  62. — Showing  the  mi- 
nute BLOOD  VESSELS  OF 
THE  VILLI  AND  INTESTINAL 
WALLS 

The  arteries  are  striped,  the  veins 
black  and  the  capillaries  open. 
(Oppel) 


THE    ABSORPTION    OF    FOODS 


116 


water  around  it  may  represent  the  blood.  Under  these  con- 
ditions there  would  seem  to  be  no  special  reason  why  there 
should  be  a  flow  of  liquid  in  either  direction;  but  nevertheless, 
as  a  matter  of  fact,  the  contents  of  the  tube  soon  begin  to 
flow  out  through  the  wall  of  the  tube  into  the  jar  and  at  the 
same  time  water  flows  into  the  tube.  They  flow  at  different 
rates  of  speed,  however,  in  the  two  directions,  the  water,  in 
this  particular  case,  flowing  into  the 
tube  much  more  rapidly  than  the 
sugar  solution  flows  out.  This  proc- 
ess is  called  osmosis. 

Since  the  membrane  contains  no 
holes  large  enough  to  be  seen  with  a 
microscope,  the  condition  in  which 
water  or  any  other  liquid  could  pass 
through  it  must  necessarily  be  that  of 
a  very  fine  state  of  division,  doubt- 
less in  what  chemists  call  molecules. 
Molecules  are  the  smallest  forms 
which  any  substance  can  take  and 
yet  maintain  its  own  characteristics 
and  are,  of  course,  invisible.     It   is 

known,  however,  that  molecules  are  of  different  sizes,  a 
sugar  molecule  containing  practically  eight  times  as  many 
parts  (atoms)  as  a  water  molecule.  If,  then,  sugar  molecules 
and  water  molecules  are  mingled  inside  the  tube,  and  only 
water  molecules  are  on  the  outside,  many  more  water  mole- 
cules are  in  contact  with  the  membrane  on  the  pure  water  side 
than  on  the  other;  for  each  sugar  molecule  takes  up  much  of 
the  space  on  the  inside  of  the  tube. 

Physicists  tell  us  that  all  molecules  are  in  very  rapid  motion, 
though  each,  in  a  general  way,  remains  in  its  own  "play- 
ground." These  molecules  of  water  and  sugar  then  are  con- 
stantly hitting  against  the  walls  of  the  membranous  tube,  and 
some  will  pass  through  the  infinitesimally  small  pores  in  it. 


Fig.     63. — Diagram    il- 
lustrating    OSMOSIS 


116  ADVANCED    PHYSIOLOGY 

Both  sugar  and  water  molecules  will  pass  through,  but  the 
sugar  molecules,  since  they  are  larger,  will  not  pene- 
trate as  fast  as  water.  Hence,  there  will  be  much 
more  water  going  into  the  tube  than  sugar  going  out. 
Nevertheless,  if  we  leave  the  tube  in  the  jar  long  enough  the 
sugar  will  continue  to  pass  out  till  the  solution  in  the  jar 
becomes  as  sweet  as  that  in  the  tube.  After  this,  no  noticeable 
exchange  occurs.  But  if  we  should  then  remove  the  water, 
which  by  this  time  would  contain  some  of  the  sugar, 
and  replace  it  with  fresh  water,  once  more  putting  the 
tube  in  it,  the  sugar  would  then  continue  passing  out.  If  we 
continued  to  renew  the  water  in  the  jar  as  fast  as  it  became 
charged  with  the  sugar  we  could  keep  the  sugar  flowing 
out  of  the  tube  into  the  water  of  the  jar  until  all  of 
the  sugar  was  gone  from  the  tube,  and  only  pure  water 
was  left  in  it. 

Food  Absorption. — Now,  this  process  of  osmosis  does  not 
fully  explain  the  manner  of  food  absorption,  but  it  does  ex- 
plain certain  phases  of  it.  Physicists  find  that  some  sub- 
stances will  thus  pass  through  membranes  while  others  will 
not.  The  former  they  call  crystalloids,  the  latter  colloids. 
Most  of  our  foods,  when  eaten,  are  of  such  a  character  that 
they  will  not  pass  through  membranes,  and  could  not  be 
taken  through  the  intestinal  walls;  but  digestion  changes 
them,  until  finally  they  are  in  a  form  that  will  readily  diffuse. 
Starches  and  proteids,  for  example,  will  not  diffuse,  while 
sugars  and  peptones  will.  Thus,  digestion  brings  the  food 
into  a  condition  in  which  it  can  be  absorbed. 

In  the  intestine  digested  food  is  on  one  side  of  the  mem- 
brane formed  by  the  epithelium  of  the  vilU,  while  on  the  other 
side  is  blood;  the  membrane  thus  has  different  liquids  moisten- 
ing its  two  sides.  Under  these  conditions  the  dissolved  food 
begins  to  flow  through  into  the  blood  vessels,  and  as  fast  as 
the  blood  present  becomes  filled  with  the  absorbed  food,  it  is 
carried  off  and  fresh  blood  takes  its  place.     This  continues 


THE   ABSORPTION    OF  FOODS 


117 


until  nearly  all  the  digested  portion  of  the  food  has  passed  out 
of  the  intestine  into  the  blood. 

But  meantime,  according  to  our  illustration,  water 
has  been  passing  from  the  blood  into  the  intestine.  Here, 
however,  the  illustration  partly  fails;  for  while  doubtless 
some  of  the  water  of  the  blood  does  enter  the  intestine,  it 
does  not  do  so  as  fast  as  it  would  in  the  illustration.  Exactly 
why  this  is  so,  physiologists  do  not  fully  know.  So  it  must  be 
conceded  that  the  real  secret  of  food  absorption  is  not  entirely 
understood,  and  we  have  merely  to  say  that  it  occurs  because 
of  the  nature  of  the  living  cells  in  the  intestinal  walls.  The 
membrane  of  the  villi  is  made  of  living  cells  and  these  cells, 
when  alive,  act  differently  from  those  of  non-living  tubes. 

CHANGES  IN  FOOD  AFTER  ABSORPTION 


We  can  now  understand  that  the 
is  to  bring  the  foods  into  such  a 
pass  through  the  intestinal  walls. 
Further  changes  occur  in  them, 
however,  after  their  absorption. 
The  proteids,  for  example,  are 
by  digestion  broken  into  very 
simple  compounds,  but  after  these 
are  taken  into  the  blood  they  are 
built  up  into  proteids  again.  Just 
where  and  how  this  occurs  is  not 
yet  known;  but  it  is  known  that 
proteids  are  abundant  in  the 
blood  although  only  the  simple 
products  of  proteid  digestion  are 
absorbed.  Somewhere,  therefore, 
they  are   reconverted.      A  further 


first  purpose  of  digestion 
condition  that  thej'  can 


Fig.  64. — A  highly  magni- 
fied VIEW  OP  THE  TIP  OF 
A    VILLUS 

Showing  the  absorption  of  fat. 
The  black  dots  are  fat. 

change  also  takes  place 


118 


ADVANCED    PHYSIOLOGY 


These  substances  are  also  taken  into  the  villi  (Fig.  64),  but 
not  into  the  blood  vessels;  they  enter  the  single  tube,  the 
lacteal,  in  the  center  of  each  villus,  and  during  their  absorption 

appear  to  be  again  united  into  true 
fat.  Although  physiologists  do  not 
know  just  where  or  how  this  occurs, 
the  fact  that  true  fat  rapidly  collects 
in  the  lacteals  during  absorption 
would  seem  to  indicate  that  the  fat  is 
broken  up  simply  to  enable  it  to  be 
absorbed  through  the  intestinal  walls. 


Thoracic 
Duct 


THE  PATH  TAKEN  BY  THE  ABSORBED 
CARBOHYDRATES  AND  PROTEIDS 


Proteid  foods  and  carbohydrates 
both  pass  directly  into  the  blood  ves- 
sels. The  veins  carrying  this  blood 
away  from  the  viccera  unite  and 
form  one  large  vessel,  called  the 
portal  vein;  this  goes  to  the  liver, 
where  it  divides  into  very  minute 
branches;  Fig.  65.  After  passing 
through  the  liver,  the  blood  collects 
once  more  and  flows  to  the  heart. 
This  portal  vein,  which  with  these 
same  relations  occurs  in  all  back- 
boned animals,  is  the  only  vein  in 
the  body  which  breaks  up  into 
branches  in  the  liver  on  its  way  to 
the  heart.  All  the  others  run  directly 
to  the  heart. 

Why  should  the  blood  from  the 
intestine  be  thus  distributed  through  the  Hver?  It  is  evident 
that  soon  after  each  meal  the  largest  amount  of  food  stuff  is 
present  in  the  portal    vein.     If  this  should    pass    immedi- 


FiG.     65. — Diagram     of 

THE  VENOUS  CIRCULA- 
TION OF  THE  INTESTINE 
AND    LIVER 


THE    ABSORPTION    OF    FOODS 


119 


ately  around  the  body,  the  various  tissues  would  have  an 
over-supply  of  foods  for  a  few  hours,  and  after  that,  until 
the  next  meal  time,  there  would  be  a  scarcity.  This  would 
be  a  very  faulty  method  of  nutrition,  since  most  of  the 
tissues  are  doing  as  much  work  at  one  time  of  the  day  as 
at  another,  and  so  need  food  all  the  time. 

The  Liver  as  a  Storehouse  for  Carbohydrates. — To  prevent 
this  irregular  supply  of  food  to  the  tissues  is  one  of  the  duties 
of  the  hver.     As  the  food-laden  blood  passes  through  it,  a  large 
part  of  the  sugar  is  changed  into  a  compound  called  glycogen, 
and  left  stored  in  the  Hver  cells;  Fig.  66.     Its  chemical  make- 
up is  the  same  as  that  of  veg- 
etable  starch.     The  blood, 
with  a  small  load  of  sugar 
leaves  the  organ,  other  food 
substances    having    under- 
gone    no     change.     After 
the     food     of     one     meal 
has   been   absorbed   from 
the    intestine,    the     liver 
begins,  little  by  little,  to 
dole  out  to  the  blood  this 
stored  sugar  so  that  the 
latter,    circulating   about  the   body,     contains   at   all   times 
about  the  same  amount.     This  uniform  supply  is  necessary 
for  the  best  health  and  most  efficient  activity  of  the  body 
organs.     Too  much  or  too  little  sugar  in  the  blood  is  injurious. 
Thus  while  the  bile  secreted  by  the  liver  is  of  little  use  in 
digestion,  the  liver  is  itself  a  highly  important  organ,  as  a 
regulator  of  the  food  supply  to  the  blood. 

PATH  TAKEN  BY  THE  FATS 

The  fats  pass  into  the  lacteals  of  the  villi  and  these  open 
into  larger  vessels  in  the  walls  of  the  intestine,  which  in  turn 
unite  with  others  to  form  still  larger  ones  (of  about  the  size  of 


Fig.  66. — Liver  Cells 

Loaded   with  glycogen    which    they    have 

made  out  of  sugar  taken  from  the  blood- 

(Modified  from  Frericha) 


120  '  ADVANCED    PHYSIOLOGY 

blood  vessels)  and  then  pass  up  through  the  mesentery. 
Thus  there  are  three  sets  of  vessels  in  the  mesentery: 
arteries  bringing  blood,  veins  carrying  food-laden  blood 
away,  and  lacteals  carrying  off  the  fat;  Fig.  65.  The 
lacteals  finally  empty  into  a  duct  which  runs  past  the 
liver  and  stomach,  through  the  diaphragm,  up  through 
the  thorax  into  the  neck  region,  a  little  above  the  heart. 
This  tube,  which  is  called  the  thoracic  duct,  finally  empties 
into  one  of  the  large  veins  which  bring  blood  bi:fck  to  the 
heart;  Fig.  65. 

The  contents  of  the  thoracic  duct  are  white  and  milky, 
due  to  the  fat  in  emulsion;  in  fact,  the  contained 
materials  are  much  the  same  as  the  chyle  in  the  intestine. 
The  lacteals,  then,  and  the  ducts  connected  with  them  act  as 
a  temporary  storehouse  for  fats.  The  flow  from  the  thoracic 
duct  into  the  large  vein  at  the  base  of  the  neck  is  slow  and 
interrupted  and  it  is  only  after  several  hours  from  the 
time  fat  enters  the  lacteals,  that  it  passes  into  the  main 
blood  system. 

The  passage  of  the  absorbed  fats  through  the  thoracic 
duct  is  not  produced  by  any  heart-like  organ.  The  simple 
pressure  of  the  surrounding  organs,  the  peristaltic  move- 
ments of  the  intestine,  the  constant  displacement  of  organs 
by  breathing  muscles — these  and  other  lesser  influences 
produce  a  slow  flow.  This  movement  can  take  place  in 
but  one  direction  on  account  of  valves  which  open  only  one 
way*  and  are  located  at  very  frequent  intervals  throughout 
the  ducts. 

Even  the  fat  in  time  gets  into  the  blood;  but  it  seems  as  if 
the  thoracic  duct  and  the  lacteals  were  designed  to  switch 
the  fat  around  the  liver  and  bring  it  to  the  blood  without 
flowing  through  that  organ.  The  liver  can  readily  store 
sugars  and  is  not  injured  by  the  proteids  passing  through  it, 
but  apparently  it  is  necessary  for  the  fats  to  reach  the  blood 
system  by  some  other  course. 


■ 

1    w^.rp 


THE    ABSORPTION    OF    FOODS  12) 


SUMMARY  OF  DIGESTION  AND  ABSORPTION 


This  finishes  the  story  of  the  entrance  of  food  into  the  body. 
The  brain  begins  the  history  by  selecting  the  food  through  the 
sense  of  taste;  heat  cooks  and  prepares  it;  the  teeth  grind  it 
I  into  fine  pulp  which,  by  means  of  the  tongue,  is  thoroughly 
mixed  with  water  and  saliva.     Then  begins  a  series  of  chemi- 
I  cal  changes  as  the  food  is  passed  through  that  chemical  lab- 
I  oratory,  the  alimentary  canal.     It  is  taken  into  this  labora- 
'  tory  as  more  or  less  solid  material  containing  proteids,  starches, 
fats  and  other  substances,  but  by  the  chemical  action  of  the 
ferments  produced  by  the  glands,  these  ingredients  are  soft- 
ened and  completely  transformed  until  they  are  almost  wholly 
''  dissolved  into  a  syrupy  white  mass,  which  does  not  bear  the 
slightest  resemblance  to  the  original  food  in  appearance,  and 
I  very  little  in  chemical  nature.     As  the  food  is  forced  along, 
I  the  villi  with  which  the  intestine  is  lined  begin  to  pick  out  of 
I  the  mass  the  useful  parts,  leaving  the  rest  in  the  canal  to  be 
i  ejected  later  as  worthless.     The  sugars  and  proteids  are  handed 
!  over  to  the  blood  vessels  which  take  them  to  the  liver  where 
a  part  of  the  sugars  is  temporarily  stored.     The  fats  are  passed 
to  the  lacteals  which  likewise  carry  them  to  the  blood,  but  by 
a  different  track,  a  side  track  as  it  were,  which  switches  them 
around  the  liver.     Finally  all  the  nutriment  gets  into  the 
blood  by  which  it  is  carried  around  the  body  to  any  part 
that  needs  it.     Digestion  and  absorption  are  thus  finished 
and    we    may    turn    our    attention   to   the  next  process — 
circulation. 


CHAPTER  IX 
THE  BLOOD  AND  ITS  FUNCTIONS 

Blood  and  blood  vessels  are  entirely  lacking  in  some  of  the 
lower  animals,  as  for  example,  in  sponges,  jelly  fishes,  corals 
and  the  lowest  of  the  worms,  the  so-called  ''flat-worms."  In 
the  insects,  too,  the  blood  system  is  present  only  in  a  weak, 
poorly  formed  way.  This  seems  particularly  strange  when 
one  considers  how  dependent  a  human  being  is  on  the  blood 
system;  so  dependent,  indeed,  that  after  a  severe  cut  a  person 
may  die  from  loss  of  blood.  Blood,  in  fact,  is  considered  the 
symbol,  if  not  the  synonym,  of  life  itself. 

By  studying  these  animals,  however,  we  find  the  reason 
why  they  do  not  need  blood  systems.  The  sponge  has  numer- 
ous pores  opening  into  the  body;  these  lead  to  canals  which 
extend  through  the  substance  of  the  animal,  thus  carrying  all 
over  the  body  the  water  and  food  substances,  which  enter 
the  canals.  At  the  same  time  the  sponge  obtains  oxygen  from 
the  water  circulating  through  the  canals.  The  jelly-fishes, 
corals  and  flat-worms  .all  have  complex  stomach  cavities; 
numerous  pouches  and  ducts  leading  away  from  the  stomach 
carry  the  food  particles  to  all  parts  of  their  bodies.  So  much 
water  is  taken  in  with  their  food  that  these  animals  obtain 
all  the  oxygen  they  need  from  the  same  water  in  which  their 
food  floats.  Insects  have  a  tubular  digestive  tract  going 
almost  straight  through  the  animal;  but  besides  this  there  is 
a  great  network  of  air  tubes  all  over  the  body,  between  the 
muscles,  passing  into  the  legs,  wings  and,  in  fact,  everywhere. 
These  bring  air  in  through  sets  of  pores  in  the  ''skin,"  and 
take  it  over  the  body.  In  the  human  being  the  digestive  tract 
is  a  tube,  with  no  side  branches  of  any  sort;  and  all  the  air  one 
^akes  in  goes  into  two  comparatively  small  sacs,  the  lungs. 

122 


THE   BLOOD   AND   ITS   FUNCTIONS  123 

Thus  animals  in  which  there  is  some  other  means  of  dis- 
tributing air  and  food  lack  the  blood  system.  We  may  con- 
clude, then,  that  one  of  the  functions  of  that  system  is  the 
distribution  of  food  and  oxygen. 

THE  BLOOD 

Blood  makes  up  about  one-thirteenth  of  the  body  weight. 
It  is  really  a  very  complex  fluid,  for  it  contains  all  of  the  food 
materials  from  the  intestine  and  also  receives  many  waste 
products  from  worn-out  parts  of  the  body.  But  leaving  aside 
these  complexities  of  chemical  composition,  we  may  learn 
by  a  study  with  the  microscope  that  fresh  blood  consists 
of  a  liquid  almost  as  limpid  as  water,  which  has  floating  in 
it  an  immense  number  of  minute,  solid  bodies.  The  liquid 
is  called  the  plasma;  the  solid  bodies  are  of  three  kinds:  red 
corpuscles  or  erythrocytes,  white  corpuscles  or  leucocytes,  and 
platelets;  Fig.  10. 

The  relative  proportion  of  these  in  the  blood  is  approxi- 
mately as  follows:  water  90%,  sohds  10%.  Of  the  soUds, 
about  72%  is  proteid  in  character,  the  remainder  consisting 
of  fats,  acids,  and  salts.  Some  of  these  are  unutilized  food 
materials,  others  the  result  of  ''wear  and  tear"  of  body  pro- 
toplasm as  it  ceaselessly,  day  in  and  day  out,  performs  its 
vital  work. 

Blood  Plasma. — The  plasma  is  a  transparent  liquid  of  a 
hght  straw  color.  It  is  the  plasma  that  gives  the  fluid  char- 
acter to  the  blood  and  enables  it  to  flow  through  the  vessels. 
Its  chemical  composition  varies.  Into  it  are  absorbed  the 
foods  from  the  intestine,  and  into  it  also  are  passed  the  various 
waste  products  from  the  body.  Its  composition  will  there- 
fore be  different  after  a  meal  from  what  it  is  after  a  period  of 
fasting.  When  one  is  resting,  too,  fewer  waste  products  are 
eUminated  to  make  the  blood  impure  than  when  one  is  actively 
working.  One  of  the  constituents  of  the  plasma  will  be  no- 
ticed later  because  of  its  important  relation  to  blood  clotting. 


124  ADVANCED  PHYSIOLOGY 

This  is  a  proteid  kno^\Ti  as  fibrinogen  which  is  so  completely 
dissolved  as  to  Se  quite  invisible. 

Red  Blood  Corpuscles.  —  Red  blood  corpuscles  are  minute 
discs,  having  a  diameter  of  about  ^^Viy  inch  (.007  mm.),  and  a 
thickness  of  1-^77-0-  inch  (.0025  mm.) .  There  are  about  5,000,- 
000  of  these  in  a  drop  of  blood  no  larger  than  the  head  of  an 
ordinary  pin.  When  freshly  drawn  from  the  body  these  loz- 
enge-shaped discs  appear  concave  on  each  side  (Fig.  10), 
but  while  circulating  in  the  vessels  they  are  frequently  cup- 
shaped.  While,  in  some  respects,  they  are  like  other  cells  in 
the  body  they  have  no  nucleus  and  no  power  of  division. 
This  absence  of  a  nucleus  is  found  only  in  a  group  of  animals 
known  as  mammals;  i.  e.  in  those  which  have  bodies  covered 
with  hair,  which  suckle  their  young,  and  which  have  distinct 
thoracic  and  abdominal  cavities  separated  by  a  diaphragm. 
Fishes,  frogs,  reptiles  and  birds  are  not  mammals,  and  their 
red  blood  corpuscles  are  nucleated. 

Each  corpuscle  consists  of  two  parts:  (1)  a  spongy  mass, 
called  the  stroma;  (2)  a  red  liquid  which  is  held  in  this  stroma 
somewhat  as  water  is  held  in  a  sponge.  The  red  color  of  the 
corpuscle  is  due  to  this  liquid,  which  is  called  haemoglobin. 
It  is  the  millions  of  these  red  corpuscles  with  their  hsemiO- 
globin  that  give  the  red  color  to  the  blood. 

Haemoglobin  is  not  always  of  the  same  color.  If  it  is 
mixed  with  plenty  of  air,  it  absorbs  a  great  deal  of  oxygen, 
becomes  a  bright,  crimson  red,  and  is  then  spoken  of  as 
oxyhaemoglobin.  This  is  its  condition  in  the  blood  in  the 
arteries.  If  the  oxygen  is  withdrawn,  however,  the  hsemo- 
globin  assumes  a  darker  color,  and  is  called  reduced  haemo- 
globin. This  is  its  condition  in  the  blood  in  the  veins  re- 
turning from  the  body  to  the  heart.  Thus  the  corpuscles  are 
turned  from  a  dark  red  to  a  bright  red  color  as  they  com^e  in 
contact  with  the  oxygen  of  the  air  in  the  lungs.  This  power 
absorbing  and  giving  up  oxygen  is  the  foundation  of  respin 
tion  and  is  dependent  upon  the  presence  of  fresh  air.    Haei 


THE    BLOOD    AND    ITS    FUNCTIONS  125 

oglobin  is  a  proteid,  but  it  differs  from  most  proteids,  in 
that  it  contains  in  addition  to  carbon,  hydrogen,  oxygen, 
nitrogen  and  sulfur,  a  little  iron. 

While  inside  living  corpuscles,  haemo- 
globin is  in  solution,  but  if  a  number  of 
corpuscles  are  treated  with  ether  and  the 
ether  evaporated,  ha3moglobin  will  be  left 
behind  in  the  shape  of  definitely  formed 
crystals;  Fig.  67.  Fig.  67.-Crystals 

It  will  be  easier  to  comprehend  the  rela-        °^  hemoglobin 

,    .    ,     , ,  ,         ,  .  FROM  RED  BLOOD 

tion  which  these  corpuscles  bear  to  a  person  corpuscles 
if  the  facts  are  stated  something  as  follows: 
In  the  blood  of  a  man  weighing  150  pounds  there  are  floating 
about  25,000,000,000,000  red  corpuscles.  These  contain  about 
one  and  one-half  pounds  of  haemoglobin,  and  their  surfaces 
equal  about  3,827  square  yards  or  the  area  of  a  surface  225  feet 
long  by  150  feet  wide.  (Compare  this  with  the  area  of  your 
school  grounds.)  The  capillaries  in  the  lungs  are  so  small  that 
these  corpuscles  pass  through  them  practically  in  single  file.  In 
this  way  a  great  area  is  exposed  for  the  absorption  of  oxygen. 
Where  does  this  great  number  of  red  corpuscles  come  from, 
and  what  becomes  of  them?  Do  they  live  as  long  as  the  rest 
of  the  body,  or  are  they  being  constantly  produced  and  de- 
stroyed? Clearly,  there  must  be  some  way  in  which  they  are 
constantly  produced,  for  a  person  may  lose  much  blood  from 
a  wound  and  recover  completely  in  a  few  days.  The  answers 
to  these  questions  are  rather  unexpected;  in  a  healthy  person 
blood  corpuscles  are  constantly  being  produced  in  the  red 
marrow  of  the  bones,  and  they  are  being  as  constantly  destroyed 
in  the  liver  and  perhaps  in  the  spleen.  Indeed,  the  bile  from  the 
liver  is,  in  part,  the  waste  from  broken  down  red  corpuscles. 
How  long  a  red  corpuscle  lives  we  have  no  means  of  knowing; 
but  it  starts  in  the  bone  marrow,  does  duty  as  an  oxygen  carrier 
for  9,  while,  and  finally  ends  its  life  in  the  liver  or  spleen. 


126  ADVANCED    PHYSIOLOGY 

White  Blood  Corpuscles. — White  blood  corpuscles  are  of  a 
transparent,  bluish  white  color  and  are  considerably  larger 
than  the  red  ones,  although  the  latter  are  about  five  hundred 
times  as  numerous;  Fig.  10.  White  corpuscles  are  real 
cells,  since  they  contain  a  nucleus,  but  they  are  constantly 
changing  their  shapes.  They  are  active  little  bodies  which 
sometimes  move  of  themselves,  independently  of  the  blood 
flow.  Any  part  of  the  white  corpuscle  may  protrude,  and  the 
entire  substance  of  the  body  be  allowed  to  flow  into  the  pro- 
trusion. By  repeating  this  process  indefinitely,  the  cor- 
puscle moves  from  place  to  place.  This  method  of  locomo- 
tion is  called  amoeboid,  after  the  amoeba,  a  microscopic  animal 
which  moves  by  the  same  method. 

In  function,  too,  the  white  corpuscles  are  different  from 
the  red.  One  of  their  chief  uses  is  to  perform  for  the  body 
duties  similar  to  those  of  street  cleaners  in  our  cities.  They 
are  not  confined  inside  the  blood  vessels,  but  may  pass  out 
into  the  tissues,  where  they  have  many  functions.  If  any 
irritating  or  injurious  substance  gets  into  the  body  under  the 
skin,  these  white  corpuscles  collect  around  it  in  great  numbers 
for  the  purpose  of  removing  it.  If  the  irritating  substance  is 
small,  the  white  corpuscles  may  be  able  to  surround  it  com- 
pletely and  then  carry  it  off  to  be  destroyed  elsewhere  in  the 
body. 

Another  useful  function  of  the  white  corpuscles  is  to  help 
protect  the  body  against  invading  disease  germs.  When 
these  tiny  enemies  make  their  entrance,  the  white  corpuscles, 
or  leucocytes,  assemble  quickly  to  do  battle  with  them.  The 
corpuscles  attack  the  bacteria,  and  may  even  carry  off  their 
dead  bodies;  Fig.  68.  Many  of  the  corpuscles,  as  well  as 
bacteria,  are  killed,  however,  and  sometimes,  indeed,  the  bac- 
teria overcome  the  corpuscles.  When  this  occurs,  the  bac- 
teria spread  through  the  body,  and  the  person  ''comes  down" 
with  the  disease.  When  the  corpuscles  are  victors,  and 
succeed  in  overcoming  the  bacteria  before  they  do  harm, 


i 


THE    BLOOD    AND    ITS    FUNCTIONS 


127 


Fig.  68. — White  blood  corpuscles 
or  leucocytes  that  have  engulfed 
bacteria 

In  those  at  a  may  be  seen  chains  of  bacteria 
such  as  cause  blood  poisoning  and  in  those  at 
b  are  some  rod  shaped  bacteria.  (Metschni- 
koff) 


one  may  have  absolutel)^  no  knowledge  that  anything  un- 
usual has  happened  in  the 
body.  Thus,  many  a  time 
in  our  lives,  these  little 
defenders  have  guarded  us 
from  dangers  about  which 
we  knew  nothing.  Some- 
times when  this  battle  is 
near  the  surface,  the  skin 
becomes  painful  and  in- 
flamed, and  later  it  may 
burst,  allowing  pus  to  es- 
cape. This  pus  is  largely 
made  up  of  white  cor- 
puscles; they  themselves 
have  died  and  are  dis- 
charged, but  they  first 
disposed  of  the  foreign  germs  that  would,  perhaps,  have  done 
us  great  injury. 

When  leucocytes  are  exhausted  they  merely  go  to   pieces 
i  and  dissolve  in  the  blood,  the  residue 
passing  out  of  the  body  through  the 
different  excretory  organs. 

Blood  Platelets.— The  third  kind  of 
solid  body  in  the  blood  is  the  platelet. 
These  platelets  are  ovoid  bodies, 
about  one-third  the  diameter  of  the 
led  corpuscles,  granular  but  color- 
less; Fig.  69  c.  They  vary  in  number 
Ijut  are  always  very  numerous  in 
unshed  blood,  600,000  or  so  in  a  single 
drop.  These  bodies  disintegrate  very 
j  quickly  after  blood  is  drawn;  so  quick- 
I  ly  that  by  the  time  a  drop  can  be 
nlaced  under  a  microscope  for  the  purpose  of  studying  themj 


Fig.  69. — Various  bodies 

FOUND  IN  blood 
a,  red  corpuscle;  b,  white  cor 
puscle  with  fibres  of  fibrin 
radiating  from  it;  c,  platelets, 
both  separated  and  in  clus- 
ters. 


128  ADVANCED    PHYSIOLOGY 

they  have  entirely  disappeared.  The  only  way  to  see  them 
at  all  is  to  draw  the  blood  into  some  preserving  fluid 
which  will  prevent  them  from  breaking  to  pieces.  The 
function  of  the  blood  platelets  is  not  definitely  known, 
although  they  probably  have  something  to  do  with  blood 
clotting. 

BLOOD  CLOTTING 

Everyone  is  familiar  with  substances  which  may  exist 
either  as  liquids  or  solids.  The  most  familiar  example  is 
water,  which  becomes  solid  if  the  temperature  falls  below  the 
freezing  point.  The  solidifying  is  dependent  on  temperature, 
and  the  material  can  be  changed  from  solid  to  liquid  by 
heating,  or  from  liquid  to  solid  by  cooling. 

So,  too,  blood  has  the  property  of  existing  in  a  liquid  and  ir 
a  solid  form.  When  it  becomes  solid,  we  speak  of  it  as 
clotted.  This  clotting,  however,  differs  decidedly  from  the 
freezing  of  water,  since  it  is  not  due  to  cooling,  for  blood  will 
clot  even  if  kept  warm.  Indeed,  the  comparison  of  clotting 
with  the  freezing  of  water  is  not  a  good  one,  for  the  blood 
greatly  changes  its  nature  when  clotting  and  can  never  be 
brought  back  again  into  the  condition  of  liquid  blood.  If 
blood  is  drawn  directly  from  the  blood  vessels  into  a  small 
dish,  it  will  be  found  at  first  to  be  fluid,  like  water;  if  allowed 
to  stand  a  few  minutes  it  becomes  jelly-like.  Presently  it 
forms  such  a  firm  jelly  that  the  dish  can  be  turned  upsidf 
down  without  displacing  any  of  the  blood.  If  it  stands  for 
some  time  longer  the  jelly  mass  will  shrink  and  a  yellowish 
liquid  ooze  out  of  it.  This  liquid  is  known  as  serum,  and  thr 
contracted  jelly,  which  holds  most  of  the  red  corpuscles,  is  tht^ 
clot.  If  now  the  clot  is  taken  out  and  thoroughly  washed  ii 
water,  all  the  corpuscles  can  be  separated  from  it,  and  the 
material  left  will  be  a  tangled  mass  of  white,  elastic  threads. 
This  substance  is  called  fibrin.  It  must  be  understood  thai 
the  fibrin  does  not  exist  while  the  blood  is  in  the  vessels,  but 


THE  BLOOD  AND  ITS  FUNCTIONS  129 

is  formed  while  the  blood  is  clotting.  Furthermore,  it  is  known 
that  blood  does  not  clot  at  all  unless  calcium  is  present  in  it. 
The  agents  involved  in  the  production  of  fibrin,  and  there- 
fore of  clotting,  may  be  shown  in  relation  to  one  another  as 
follows : 
Thrombokinase  (from  tissue  juice,  white  corpuscles  or  platelets) 

+  Thrombogen  (from  plasma) 
+  Calcium  salts  (from  plasma) 
=  Thrombin  =  Fibrin  ferment 
Thrombin  +  Fibrinogen  (in  solution  in  blood) 
=  Fibrin  (insoluble) 

We  have  already  noted  that  in  the  blood  plasma  there  is  a 
proteid  called  fibrinogen  (see  page  124).  This  is  dissolved  in 
the  Hquid,  and  is  no  more  visible  than  the  sugar  in  a  cup  of 
coffee.  It  is  from  this  fibrinogen  that  the  fibrin  is  produced. 
Fibrinogen,  however,  will  not  give  rise  to  fibrin  if  left  to 
itself,  but  if  a  certain  amount  of  material  called  thrombin, 
or  fibrin  ferment,  is  present,  it  at  once  breaks  up  into  two 
substances;  one  of  these  remains  in  solution  in  the  blood,  but 
the  other  is  not  soluble,  and  appears  at  once  as  fibres  form- 
ing the  fibrin.  Hence  blood  clotting  is  due  to  the  formation 
of  fibrin  out  of  fibrinogen  under  the  influence  of  fibrin  ferment. 

Whence  comes  this  fibrin  ferment?  Since  the  blood  will 
not  clot  when  flowing  through  the  arteries  and  veins,  we  con- 
clude that  this  ferment  cannot  be  present  in  living  blood.  It 
must  be  formed  when  the  blood  is  drawn.  Its  source  is  not 
certainly  known  but  there  are  strong  reasons  for  believing 
that  three  different  agents  are  involved: 

(a)  thrombokinase  (from  white  corpuscles,  platelets,  or 
the  cut  tissues) ; 

(b)  thrombogen  (from  the  plasma)  and 

(c)  calcium  salts. 

When  these  three  factors  are  present  at  the  same  time,  blood 
clots  quickly,  and  thus  we  conclude  that  they  form  the  sub- 
stance    which     changes     fibrinogen     into     fibrin.       At     all 


130  ADVANCED    PHYSIOLOGY 

events,  it  is  an  undisputed  fact  that  while  blood  is  flowing 
through  the  vessels,  it  contains  no  fibrin  ferment,  and  con- 
sequently the  fibrinogen  remains  unchanged;  but  as  soon  as 
the  blood  comes  into  contact  with  any  material  other  than 
the  regular  lining  of  the  blood  vessels,  fibrinogen  at  once 
changes  to  fibrin  and  the  blood  clots.  Even  contact  with 
other  tissues,  e.g.  muscle  or  skin  of  the  same  animal,  pro- 
duces a  clot  almost  immediately;  so,  too,  will  an  injury  to  a 
blood  vessel  or  simple  exposure  of  blood  to  the  air. 

At  times  when  it  is  desired  to  prevent  blood  from  clotting, 
this  can  be  done  by  adding  to  it  certain  chemicals,  e.g.  sodium 
sulfate  or  magnesium  sulfate,  pepsin,  trypsin  or  peptones;  the 
extracts  of  the  salivary  glands  of  leeches  or  snake's  venom  will 
very  effectually  prevent  clotting.  Rapid  cooling  will  retard 
and  sometimes  entirely  check  it.  Blood  can  be  made  to  clot 
more  rapidly  by  bringing  it  into  contact  with  foreign  sub- 
stances, for  example,  by  covering  with  cloth  a  wound  from 
which  it  is  flowing. 

Purpose  of  Blood  Clotting. — Blood  clotting  is  nature's 
method  of  checking  the  flow  of  blood  from  wounds,  thus  pre- 
venting possible  fatal  consequences.  All  our  lives  we  are 
thus  guarded,  not  only  from  annoyance  from  small  injuries, 
but  from  the  very  serious  results  which  would  follow  from  bad 
accidents  or  from  surgical  operations. 

DISEASES  OF  THE  BLOOD 

It  is  often  affirmed  that  a  person's  health  is  poor  because 
his  blood  is  ''out  of  order"  or  needs  "toning  up."  In  most 
cases,  this  is  a  mistake.  Health  is  not  determined  by  the  con- 
dition of  the  blood,  but  on  the  contrary  the  state  of  the  blood 
is  determined  by  the  rest  of  the  body.  The  blood  may  not  be 
in  good  condition,  it  is  true,  but  the  reason  is  usually  be- 
cause the  living  cells  of  the  rest  of  the  body  are  out  of  order. 
For  example,  a  person  is  pale  and  white  and  suffers  from  lassi- 
tude  and   other   uncomfortable  symptoms.     The  physician, 


THE    BLOOD    AND    ITS   TTJNCTIONS  131 

perhaps,  makes  an  examination  of  the  blood  and  finds  that  he 
has  ancemia,  and  that  the  blood  contains  too  few  red  corpus- 
cles. Now,  while  in  this  case  it  is  true  that  the  trouble  shows 
itself  in  the  blood,  the  real  cause  is  not  there,  but  in  those 
parts  of  the  body  where  the  red  corpuscles  are  formed, 
and  which  for  some  reason  are  not  making  them  rapidly 
enough.  Suppose  again  the  paleness  to  be  due  to  too  many 
white  corpuscles.  Here  too,  while  the  most  noticeable 
feature  is  in  the  blood,  the  real  cause  is  in  some  of  the  other 
organs  whose  impaired  functions  result  in  increasing  the 
numbers  of  white  corpuscles  until  they  are  altogether  too 
numerous.  The  physician's  treatment  should  be  directed  to 
the  real  source  of  the  trouble,  not  to  the  blood  itself. 

Blood  Poisoning. — Blood  poisoning  is  a  name  given  to  a 
series  of  troubles  caused  by  a  certain  kind  of  bacteria  which 
get  into  the  body  and   multiply  rapidly.      The 
poisoning   agents    are    commonly    in    the    skin,     «— HJJN^ 
muscles,  glands  or  some  other  active  organ,  not  ^••'c. 

often  in  the  blood  itself;  but  in  some  forms  of         \i* 
the  disease  the  blood  carries  them  through   the     ^%kfLj^  , 
body  and  hence  the  name  blood  poisoning  arises.     ^^^H 
The  germs  which   cause    the   trouble    (Fig.   70) 
are  abundant  everywhere,  in  the  air,  in  the  soil,     rp^^   g^*^_ 
on  our   clothes,  on  our  skin,  etc.     They   do  no     teria  that 
harm,  unless  they  penetrate  the  skin  by  way  of  a     produce 
cut  or  bruise;  and  even  then  they  do  not  often      various 
cause    trouble,    for  our  bodies   are    wonderfully      ^^rms  of 

-  1  .    ,  n  .       .  1  r^  blood     POI- 

endowed  with  power  for  resisting  them.     Com-      g  q  n  i  n  g 
monly,  therefore,  they  either  do  us  no  injury  or      boils   etc. 
produce  simply  a  slight  pimple,  a  little  festering     a,  streptococci; 
sore  or  a  boil.     If  the  body  is  in  good  condition,      ^^.  '°^  ^ 
the    white    corpuscles    attack    the    bacteria    in 
these  sores,  and  with  the  help  of  other  resisting  agencies  the 
germs  are  destroyed  and  the  sore  heals.     But  in  other  cases, 
either  where  the  resistance  of  the  body  is  very  weak  or  the 


132  ADVANCED    PHYSIOLOGY 

germs  are  very  strong,  the  germs  are  not  checked  in  their 
growth,  but  continue  to  multiply  rapidly  and  are  distributed 
by  the  blood,  producing  serious  and  even  fatal  results.  Blood 
poisoning,  as  we  call  it,  may  thus  be  a  very  serious  matter,  but 
it  is  similar  in  nature  to  the  smaller  troubles,  e.g.  festers,  boils 
and  the  soreness  that  follows  skin  woundSo 

In  endeavoring  to  avoid  all  forms  of  blood  poisoning  we 
should  remember  a  few  simple  facts:  (1)  The  discharges 
(pus)  from  sores  or  boils  are  sure  to  contain  disease  germs 
and  they  should  by  every  means  be  kept  from  coming  in  con- 
tact with  fresh  cuts  or  bruises.  (2)  Whole,  uninjured  skin  is 
a  sufficient  protection  for  the  parts  underneath  and  germs 
cannot  penetrate  it.  But  all  points  where  the  skin  is  broken, 
cuts  and  bruises,  should  be  carefully  cleansed  in  boiled  water. 
(3)  Various  disinfecting  ointments  contain  substances  which 
kill  the  germs.  These  ointments  are  of  extreme  value  in 
cases  where  the  skin  is  broken.  A  wash  of  carbolic  acid,  one 
part  to  twenty  of  water,  is  an  excellent  one  to  keep  on  hand,  and 
to  use  freely  for  washing  all  cuts,  bruises  or  deep  scratches. 

Malaria. — Malaria,  chills  and  fever,  and  fever  and  ague  are 
all  practically  the  same  disease.  Here  we  have  an  actual  dis- 
ease of  the  blood,  for  it  is  due  to  a  minute  parasite  that  lives 
upon  the  red  corpuscles  and  in  no  other  part  of  the  body.  These 
parasites  kill  the  corpuscle,  which  then  breaks  to  pieces,  and 
the  parasites  come  out  into  the  blood  plasma.  At  this  time, 
a  little  poison  is  let  out  into  the  blood  from  the  broken  cor- 
puscle, producing  a  chill,  followed  by  a  fever.  Soon  after, 
the  parasites  attack  other  corpuscles,  grow  forty-eight  hours 
and  break  up  again.  Thus,  this  peculiar  disease  is  intermittent ; 
i.e.  comes  with  regularity  at  certain  intervals.  If  there  is  a 
small  amount  of  quinine  in  the  blood  at  the  time  the  corpuscles 
break  up,  the  little  parasites  will  be  destroyed  and  the  disease 
checked.  Hence  quinine  is  almost  always  used  as  a  medicine  in 
cases  of  malaria. 

One  of  the  most  valuable  discoveries  of  science  has  been 


THE    BLOOD    AND    ITS    FUNCTIONS 


133 


the  method  by  which  these  Uttle  parasites  find  their  way  into 
the  blood.  They  cannot  pass  directly  from  person  to  person 
and  hence  the  disease  is  not  contagious.  It  used  to  be  sup- 
posed that  malaria  came  from  bad  air,  especially  from  the  air 
of  swamps,  night  air  being  thought  particularly  dangerous. 


Surface  ofWai-er 


Fig.  71. — Mosquitoes 

Figures  a  and  6  show  the  larvae  in  water,  a  being  the  harmless  species  (Culex)  and 
h  (Anopheles)  the  species  that  carries  malaria.  At  c  is  shown  the  position  assumed 
by  the  harmless  type  upon  alighting,  and  at  d  the  position  of  the  dangerous  one.  In 
the  latter  it  will  be  seen  that  the  body  and  head  are  in  one  straight  line  while  in  the 
harmless  species  the  body  is  bent  at  the  neck.  At  e  is  shown  the  dangerous  Anophe- 
les with  spotted  wings  and  five  hair-hke  projections  (or  feelers)  in  front;  at  /  the  Cu- 
lex with  plain  wings  and  three  feelers. 

P]      But  these  theories  have  been  disproved.     It  has  been  found 
that  these  parasites  live  in  a  certain  kind  of  mosquito.     If 


134 


ADVANCED    PHYSIOLOGY 


a  female  mosquito  bites  a  patient  suffering  from  malaria 
it  will  suck  some  of  the  red  corpuscles  containing  the  parasites 
into  its  body.  In  the  mosquito  these  parasites  go  through 
some  changes  and  finally  come  to  lodge  near  its  mouth.  If 
this  mosquito  later  bites  another  person,  the  tiny  parasites 
are  likely  to  be  inoculated  into  the  body  where  the  skin  is 
pierced.  Thus  a  second  person  is  infected.  This  is  the  only 
method  by  which  malaria  is  known  to  be  distributed.  Hence 
any  means  of  getting  rid  of  mosquitoes  is  a  protection  against 
malaria.  Mosquito  netting  at  windows  and  doors  is  a  very 
efficient  protection  from  this  disease.  Draining  puddles  and 
pools  and  emptying  all  barrels  of  standing  water  where  mos- 
quitoes breed  is  another.  Only  one  kind  of  mosquito  dis- 
tributes the  disease  and  fortunately  this 
is  not  the  most  common  kind.  A  method 
of  distinguishing  it  from  the  harmless  species 
is  explained  in  Figures  7 1  and  72. 

Yellow  Fever. — Yellow  fever  is  fortunately 
uncommon  in  this  country,  occurring  only 
at  rare  intervals  in  the  southern  states.  In 
tropical  countries,  e.g.  South  America  and 
the  West  Indies,  it  is  of  more  frequent 
occurrence.  Occasionally  it  does  get  into 
our  southern  cities  in  the  summer,  and 
in  past  years  it  has  produced  very  serious 
epidemics  with  thousands  of  deaths.  Its 
cause  has  recently  been  discovered  to  be 
an  extremely  minute  unicellular  organism.  It 
is  mentioned  here  because,  like  malaria,  it  is 
known  to  be  distributed  by  mosquitoes,  though  the  species 
carrying  yellow  fever  germs,  Stegomyia,  is  not  the  same  as  the 
one  which  spreads  malaria. 

These  facts  show  clearly  that  mosquitoes  are  among  our 
most  deadly  enemies.  The  different  states  of  the  Union  are 
showing   appreciation   of  this    fact    by    appropriating    con- 


FiG.    72.  — Mos- 
quitoes 

g,  Anopheles,  h, 
Oulex,  as  they 
alight  on  the  walla 
of  a  room. 


THE    BLOOD    AND    ITS    FUNCTIONS  135 

siderable  money  for  the  warfare  against  mosquitoes.  Since 
mosquitoes  breed  in  stagnant  water,  the  draining  of  such 
breeding  pools  or  the  pouring  of  kerosene  on  the  surface  is  an 
efficient  method  of  kilUng  the  young.  Everyone  for  his  own 
jood,  as  well  as  for  the  good  of  others,  should  give  all  the 
5sistance  he  can  to  this  work  of  mosquito  extermination. 

Influenza. — While  this  disease  is  doubtless  acquired  by 
wreathing  in  the  organisms  causing  it,  it  manifests  itself  prim- 
rily  as  a  disturbance  of  the  blood  in  the  form  of  a  fever.  As 
well  known,  it  is  extremely  contagious,  and  thus  easily 
ssumes  the  proportions  of  an  epidemic.  It  differs  from  an 
Ordinary  cold  by  spreading  even  more  rapidly,  in  causing  a 
)erson  to  feel  suddenly  weak,  experience  pain  in  the  head, 
)ack  or  eyes,  develop  a  fever  and  ''feel  sick'^  to  a  greater 
degree.  As  to  its  cause,  several  bacteria  have  been  recog- 
nized as  present,  and  the  practice  of  inoculation  against  the 
disease  has  been  begun  with  fairly  successful  results.  How- 
ever, immunity  is  very  transitory,  and  one  may  "catch'^ 
influenza  repeatedly.  Fatal  results  seldom  accompany  the 
malady  by  itself,  but  it  leaves  the  system  weakened  and 
susceptible,  so  that  other  more  serious  diseases,  e.g.  pneu- 
monia, are  very  liable  to  follow.  Extreme  care  while  con- 
valescing should  be  observed. 

Influenza  is  doubtless  spread  by  the  ''droplet  method ;'* 
i.e.  a  healthy  person  breathes  in  minute  moisture  droplets, 
containing  the  germs,  which  have  been  expelled  by  a  sick 
or  near-sick  person  while  sneezing,  coughing,  talking,  or  sing- 
ing. One  should  avoid  crowded  rooms,  cars,  public  gather- 
ings of  all  kinds,  and  contact  with  the  sick;  also  spend  as 
much  time  as  possible  in  the  open  air  in  recreative  exercise. 
If  attending  those  sick  with  influenza,  one  should  always 
wear  a  gauze  cloth  over  the  nose  and  mouth  as  a  precaution. 


CHAPTER  X 


THE  HEART  AND  THE  BLOOD  VESSELS 


The  heart  has  been  recognized  as  an  important  organ  for  a 
longer  time  than  any  other  part  of  the  body,  and  numerous 
phrases  in  hterature  show  the  fanciful,  as  well  as  mistaken, 
ideas  once  held  concerning  its  function.  The  expression  '4ove 
with  all  one's  heart"  is  an  example  of  the  erroneous  notion 
that  the  heart  has  something  to  do  with  the  emotions.  In  real- 
ity the  heart  has  but  one  function:  it  simply  pumps  the  blood. 
Location  of  the  Heart. — The  heart  is  located  in  the  thorax, 
between  the  lungs,  just  a  little  to  the  left  of  the  mid-line,  and 
back  of  the  ''breast  bone."  The  rigidity  of  this  bone  prevents 
one's  feeling  the  heart  under  it,  but  the  lower  end  of  it  pro- 
duces a  distinct  ''beat"  which  can  be  felt  and  seen  between 
the  fifth  and  sixth  ribs.  It  is  swung  freely  in  the  thoracic 
cavity,  attached  to  its  upper  wall  by  masses  of  connective 

tissue,  which  also  bind  it 
to  the  large  arteries  and 
veins,  and  to  the  wind- 
pipe. 

The  Coverings  and 
Structure  of  the  Heart. — 
The  heart  is  completely 
enveloped  by  a  two- 
layered  bag,  the  pericar- 
dium (Fig.  73),  which  is 
pierced  only  by  the  large 
arteries  and  veins  leaving 
and  entering  the  organ. 
The  inner  layer  of  the  pericardium  is  grown  fast  to  the  heart 
jDUScle^   and  thus  forms  a  firm,  tou^h  covering  for  it^  th§ 

m 


Tracfi 


ea 


f^ncarefionj 


Fteura 


Fig.  73. — Diagram 

Showing   the  relations  of   heart,    lungs  and 
membranes  around  them. 


THE    HEART   AND    THE    BLOOD    VESSELS  137 

outer  layer  is  loose,  the  two  moving  freely  over  each  other. 
These  pericardial  layers  are  covered  by  glandular  epithelium 
which  secretes  a  fluid  into  the  space  between  them,  this  liquid 
being  naturally  called  the  pericardial  fluid.  Were  it  not  for 
this  fluid,  the  ever-moving  heart  would  rub  against  the  sur- 
rounding tissues,  producing  much  friction  and  inflammation. 

A  person's  heart  is  about  the  size  of  his  fist.  In  shape  it  is 
something  Hke  a  strawberry  and  lies  with  the  small  end,  or 
apex,  pointing  downward  and  toward  the  left;  the  upper  end 
is  called  the  base  and  here  the  large  arteries  leave  and  the 
veins  enter  it.  It  is  a  hollow  organ,  the  walls  of  which  are  com- 
posed mainly  of  muscle;  on  the  outside  more  or  less  fat  is 
usually  deposited,  especially  in  certain  depressions  where  the 
arteries  and  veins  emerge,  and  along  grooves  which  extend 
lengthwise  or  obUquely  on  the  organ  over  places  whert  par- 
titions run  in  the  interior. 

The  cavity  of  the  heart  is  divided  by  a  vertical  wall  into 
right  and  left  chambers;  and  each  of  these  is  again  partially 
divided  into  an  upper  portion,  the  auricle,  and  a  lower,  the 
ventricle.  Each  of  these  four  chambers  is  lined  with  a  smooth 
glistening  sheet  of  membranous  epithelium,  which  keeps  the 
blood  from  direct  contact  with  the  muscle  tissues  of  its  walls. 
The  walls  of  the  auricles  are  very  much  thinner  than  those  of 
the  ventricles  and  the  wall  of  the  left  ventricle  is  thicker  than 
that  of  the  right. 

THE  EVENTS  OF  A  HEART  BEAT 

We  can  best  learn  the  structure  and  action  of  the  heart  if 
we  trace  the  flow  of  blood  through  it,  noticing  how  the  valves 
are  closed  and  opened  so  that  the  blood  always  flows  onward. 
The  blood  is  brought  from  the  body  to  the  heart  through  two 
large  veins,  which  open  into  the  right  auricle — the  superior 
vena  cava,  bringing  the  blood  from  the  upper  part  of  the  body, 
l^nd  the  other,  the  inferior  vena  cava,  bringing  it  from  the 


138 


ADVANCED  PHYSIOLOGY 


lower  part;  Fig.  74.  If  we  begin  our  description  at  the  rest 
period  of  the  heart,  i.e.  the  period  between  any  two  beats,  we 
shall  find  that  the  blood  flowing  in  these  veins  passes  in  a  large 


Inferior  Vena 
Coya 


Superior  Vena 
Cava 


Putmqnartf  Arfertf 


Tricuspid 

Valve    Oppn^^^ 


SemiLunar 
v     Vaiye  •  Closed 

CAordaeTendin& 

\Papillaru  ffusdet  T- 

Tricutpid  Yalye 
Chsed 


B 


Fig.   74. — Diagram 

Showing  the  mechanism  of  the  heart.  At  A  is  shown  the  right  side  of  the  heart 
at  the  period  of  rest,  and  at  B  the  arrangement  of  the  valves  when  the  heart 
contracts.    The  arrows  show  the  direction  of  the  blood  flow. 


stream  directly  into  the  right  auricle  (Fig.  74),  whence  it 
flows  freely  through  the  wide  opening  from  the  auricle  into  the 
ventricle.  Thus  the  auricle  and  ventricle  are  both  filling  at 
the  same  time. 

The  opening  between  the  right  auricle  and  right  ventricle 
is  guarded  by  three  flap-like  membranes,  attached  at  the  top 
of  the  ventricle;  when  the  ventricle  is  empty,  they  hang  down 
loosely  (Fig.  74  A),  but  as  the  entering  blood  collects  in  the 
bottom,  these  flaps  float  on  its  surface.  This  condition  lasts 
only  for  a  fraction  of  a  second,  when  the  muscles  in  the  walls 
of  the  auricle  contract,  forcing  all  the  blood  into  the  ventricle 
with  a  rush.  Carrying  the  flaps  on  its  surface,  the  blood  rises 
rapidly  until  the  ventricle  is  completely  filled.  At  this  time 
the  valves  are  lifted  up  directly  across  the  opening  from  the 
auricle;  Fig.  74  B.  They  are  of  such  size  and  shape  that 
when  in  this  position  they  exactly  fill  the  opening,  completely 


THE  HEART  AND  THE  BLOOD  VESSELS 


139 


preventing  the  passage  of  any  blood  back  into  the  auricle. 
These  valves  between  the  chambers  of  the  right  side  of  the 
heart  are  called  the  tricuspid  valves. 

Next,  the  muscles  in  the  walls  of  the  ventricle  contract, 
pressing  upon  the  blood  until  the  ventricle  is  emptied.  In 
what  direction  will  the  blood  flow?  It  would  go  back  into 
the  auricle  if  the  tricuspid  valve  had  not  closed  the  opening 
in  that  direction.  These  valves  are  only  soft  membranes, 
and  one  would  suppose  that  they  might  give  way  under  the 
pressure  of  blood  in  the  ventricle  and  turn  back  into  the 
auricle.  To  prevent  this,  stout  cords  (chordae  tendinae)  are 
attached  to  the  edges  of  the  valves  (Fig.  74),  their  other 
ends  being  fastened  below  to  the  walls  of  the  ventricle. 
These  cords  are  of  such  lengths  that  when  the  valves  are 
stretched  across  the  opening  the  cords  are  tight;  Fig.  74  B, 
It  would  not  be  possible  to  push  the 
valves  up  into  the  auricle  without 
breaking  these  cords;  moreover  they 
can  be  drawn  downward  somewhat 
by  Uttle  muscles  attached  to  their 
lower  ends,  the  so-called  papillary 
muscles.  As  the  ventricle  contracts, 
then,  the  blood  must  find  another 
outlet. 

The  only  real  outlet  from  the  right 
ventricle  is  a  large  artery  shown  in 
Figure  74,  and  called  the  pulmonary 
artery,  since  it  leads  to  the  lungs. 
This  artery  is  already  filled  with 
blood,  also  under  pressure,  blood  that 
would  readily  flow  back  into  the 
heart  were  it  not  for  a  set  of  valves 
preventing  such  a  return;  these,  called  the  semilunar  valves, 
consist  of  three  soft  folds  in  the  shape  of  half-cups  or 
pockets  with  their  open  ends  directed  away  from  the  cavity 


Fig.  75. — The  pulmonary 
artery  cut  open  to 
show    the     semilunar 

VALVES. 


140 


ADVANCED  PHYSIOLOGY 


of  the  ventricle;  Figs.  74  and  75.  When  the  blood  in  the 
pulmonary  artery  starts  to  run  back  into  the  empty  ventricle, 
it  fills  these  little  cups,  causing  them  to  swell  until  the  three 
stretch  completely  across  the  lumen  of  the  artery,  thus 
wholly  blocking  the  passage  and  preventing  any  backward 
flow  of  blood.  But  when  the  ventricle  contracts,  blood  is 
pushed  against  the  cups  from  below  until  it  finally  flattens 
them  against  the  walls  of  the  artery  so  that  blood  can  pass 
them  easily.  These  cup-like  flaps  remain  flattened  against 
the  walls  of  the  pulmonary  vessel  as  long  as  the  contraction 
3f  the  ventricle  forces  the  blood  onward. 

After  the  ventricle  has  contracted  as  much  as  it  can  and 
has  squeezed  out  practically  all  the  blood  it  contained,  the 

muscles  in  its  walls  relax,  leav- 
ing the  cavity  free  to  fill 
once  more.  The  blood  which 
has  just  been  forced  into  the 
artery  starts  to  flow  back  but 
immediately  fills  the  semilunar 
valves,  which  then  block  its 
backward  passage.  This  action 
can  be  better  understood,  if 
compared  to  the  behavior  of 
an  umbrella  in  a  wind.  When 
pointing  into  the  wind  it  offers 
little  or  no  resistance  to  the 
currents  of  air,  which  would 
tend  to  close  it;  but  if  turned 
the  other  way,  it  is  immediately 
opened  and  filled,  thus  blocldng 
the  passage  of  the  wind.  The  blood  cannot  flow  back  into 
the  ventricle  but  as  the  ventricle  relaxes,  the  tricuspid 
valves  fall  down  loosely  into  the  ventricle  again,  thus  allow- 
ing more  blood  to  enter  it  from  the  auricle  and  reinstating 
the  condition  with  which  we  started. 


Fig.  76.— Diagram 

Showing  the  veins  entering  and  the 
arteries  leaving  the  left  side  of  the 
heart.    Broken  line  marks  the  aorta. 


THE    HEART   AND    THE    BLOOD    VESSELS  141 

The  blood  that  flows  out  of  the  right  ventricle  goes  through 
le  pulmonary  artery  to  the  lungs,  whence  it  goes  through 
mr  vessels  called  the  pulmonary  veins  to  the  left  auricle  of 
le  heart;  Fig.  76.  The  left  side  of  the  heart,  which  the 
ilood  now  enters,  is  almost  exactly  like  the  right  side;  there 
a  similar  flap-like  valve  hanging  down  between  the  auricle 
and  ventricle.  This  mitral  valve  has  two  flaps  instead  of 
three,  but  its  action  is  precisely  the  same  as  that  of  the  tricus- 
pid. A  large  artery  also  leads  out  of  the  left  ventricle,  its 
opening  guarded  by  three  semilunar  valves,  exactly  like 
those  at  the  origin  of  the  pulmonary  artery.  This  artery 
into  which  blood  is  pumped  by  the  left  ventricle  is  called  the 
aorta,  and  through  branches  of  it,  as  we  shall  see,  blood  is 
distributed  over  the   entire   body. 

Rate  of  Heart  Action^ — The  beat  of  the  heart  is  really  very 
rapid,  a  whole  beat  occupying  less  than  a  single  second. 
About  seventy  times  a  minute,  day  and  night,  the  heart  goes 
through  the  entire  act  of  opening  and  closing  its  several  valves 
and  forcing  along  the  blood.  The  two  sides  beat  at  exactly 
the  same  time,  so  that  with  each  beat  a  small  cupful  of  blood 
is  forced  into  the  pulmonary  artery  from  the  right  ventricle  and 
a  similar  amount  from  the  left  ventricle  into  the  aorta.  The 
actual  beat  of  the  heart,  i.  e.  the  contraction  of  the  muscles 
to  force  the  blood  along,  takes  only  about  0.3  of  a  second. 
After  the  beat,  the  heart  rests  during  the  time  that  the  auri- 
cles are  filling  from  the  veins.  This  time,  which  is  the  only 
rest  the  heart  has  from  its  continual  work,  is  about  0.5  of  a 
second.  The  beating  period  is  called  the  systole,  and  the 
resting  period,  the  diastole. 

Heart  Sounds. — If  one  places  his  ear  over  a  person's  heart 
when  it  is  beating  normally,  or  if  an  instrument  constructed 
for  the  purpose  (the  stethoscope)  is  applied  to  the  area  above 
the  heart,  each  beat  seems  to  be  accompanied  by  two  sounds, 
one  longer  than  the  other.     When  a  he^rt  beat  begins  and  the 


142  ADVANCED  PHYSIOLOGY 

blood  rushes  into  the  ventricle  from  the  auricle,  the  curtain' 
like  valves  lie  in  line  with  the  current,  just  as  a  flag  flies  ou" 
in  the  current  of  the  wind.  Although  the  wind  may  be  steady, 
the  flag  ''flaps"  from  side  to  side.  So,  in  the  heart,  we  ca: 
imagine  the  mitral  and  tricuspid  valves  wavering  in  the  cur 
rent  of  blood,  even  if  it  is  steady.  This  is  thought  to  be  th 
cause  of  the  first  sound. 

The  second  sound,  following  closely  on  the  first,  is  sharper 
and  shorter.  It  is  believed  to  be  caused  by  the  closing  of  the 
semilunar  valves  in  the  large  outgoing  arteries.  These,  it  is 
thought,  are  thrown  into  their  tense,  filled  condition  so  sud- 
denly that  they  give  rise  to  a  distinct  impact  and  noise,  just 
as  doors  do  when  they  suddenly  close  in  a  current  of  wind, 
even  though  they  may  be  fitted  with  appliances  for  pre- 
venting their  actual   "slamming." 

The  Throb  at  the  Breast,  and  the  Pulse. — When  the  heart 
beats,  the  apex  is  turned  distinctly  forward  with  sufficient 
force  to  lift  the  body  wall  between  the  fifth  and  sixth  ribs, 
and  at  this  point  a  throb  is  easily  felt.  Every  time  the  heart 
beats  a  small  amount  of  blood  is  forced  into  the  arteries. 
This  fills  those  near  the  heart  more  full  of  blood  than  else- 
where; consequently  a  wave  of  pressure  travels  rapidly  along, 
causing  a  slight  swelhng  of  the  arteries  on  its  way.  If  the 
fingers  be  placed  on  the  artery  of  the  wrist,  where  it  comes 
near  the  surface,  this  wave  can  be  felt,  and  is  called  the  pulse. 
The  pulse  is  due  to  a  temporary  increase  in  the  diameter  of 
the  artery,  and  is  not  as  it  seems  to  be,  a  little  jet  of  blood 
flowing  through  the  artery  at  the  point  where  the  pulse  is 
felt.  The  pulse  can  be  felt  in  any  of  the  arteries  which  come 
near  the  surface;  but  as  arteries  are  commonly  deeply  im- 
bedded in  the  muscles,  there  are  only  a  few  places  aside  from 
the  wrist  where  it  is  evident,  e.  g.  the  neck,  and  about  the 
temple,  back  of  the  eye.  By  feeling  the  pulse  a  physician 
can  determine  the  rate  of  the  heart  beat  as  well  as  its 
force.    The  normal  rate  is  72  per  minute. 


THE    HEART   AND    THE    BLOOD    VESSELS  143 

The  heart  action,  however,  undergoes  an  interesting  change 
of  rate  with  age,  the  average  rate  found  in  large  numbers  of 
instances  being  as  follows :  In  early  babyhood,  140  beats  per 
minute.  In  childhood,  100  per  minute.  In  youth,  90  per 
minute.  In  adults,  75  per  minute.  In  elderly  persons,  70 
per  minute.    In  very  aged  persons,  75  to  80  per  minute. 

The  Work  Done  by  the  Heart. — The  muscular  power  of  the 
heart  is  very  great.  The  work  it  does  during  one  day  is  about 
equal  to  the  additional  energy  expended  by  a  man  in  climbing 

ito  the  top  of  a  mountain  3600  feet  high.  Assuming  that  the 
man  weighs  about  150  pounds,  this  would  be  equal  to  an 
amount  of  energy  sufficient  to  lift  90  tons  to  a  height  of 
three  feet.  The  work  of  the  left  side  is  greater  than  that  of 
the  right,  since  the  former  has  to  drive  the  blood  all  over  the 
body,  while  the  latter  has  only  to  force  it  through  the  lungs 
which  are  near  by.  For  this  reason  the  muscle  walls  of  the 
right  are  much  thinner  than  those  of  the  left  ventricle. 

Defects  in  the  Heart  Mechanism. — We  can  readily  see  how 
a  very  slight  injury  to  the  heart  might  result  seriously.  Sup- 
pose, for  example,  that  the  valves  should  fail  to  close  the  pas- 
sages over  which  they  are  placed  as  guards.  In  some  cases  of 
heart  disease,  a  bit  of  clotted  blood  collects  on  the  edges  of 
the  valves,  preventing  their  perfect  closure,  causing  a  leakage 
and  seriously  interfering  with  the  action  of  the  heart.  It 
appears  that  the  serious  disease,  influenza,  may  frequently 

j  affect  the  heart  muscles  and  valves,  causing  faulty  action  and 
thus   menace   the   general   health.     But  one  must  not  think 

I  that,  because  he  has  a  pain  around  the  heart,  he  is  suffer- 
ing from  heart  disease.  Indeed,  it  often  happens  that  those 
who  have  some  defect  in  the  heart  mechanism  are  quite 
unconscious  of  the  fact,  since  the  effects  are  generally  more 

i  noticeable  elsewhere. 


144 


A.DVANCED  PHYSIOLOGY 


CAUSE  AND  REGULATION  OF  HEART  BEAT 


Brain 


'  Vaqus. 
\5(pnpathetvs 


What  makes  the  heart  beat?  No  one  as  yet  understands 
life  sufficiently  to  give  a  satisfactory  answer  to  this  question, 
but  we  do  know  that  most  activities  are  brought  about  at  the 
command  of  the  brain;  most  of  the  muscles  will  not  contract 
at  all  unless  it  orders  them  to  do  so.  How  is  it  with  the  heart? 
Does  it  need  orders  from  the  brain  or  can  it  direct  its  own 
beating?  That  it  can  act  independently  of  the  brain  has 
been  shown  in  the  instances  of  many  animals,  where  the 
heart  has  been  entirely  removed  from  the  body  and  has  yet 
continued  to  beat  for  a  considerable  length  of  time,  even  so 

long  as  two  days.  Evidently  then, 
the  heart  contains  in  itself  some 
agency  that  causes  it  to  beat. 

The  heart  is  thus  automatic 
and  would  of  itself  continue  to 
beat  regularly  through  life;  but 
such  regularity  would  be  very 
unsatisfactory,  for  the  amount 
of  blood  which  the  working  or- 
gans need  varies  at  different 
times.  When  the  muscles  are 
active  they  need  much  blood, 
when  they  are  quiet  they  need 
little.  When  one  is  asleep,  the 
organs  need  less  blood  than  when 
he  is  awake,  and  all  through  life 
occasions  are  constantly  occur- 
ring where  the  body  demands  a 
more  or  less  rapid  circulation 
of  blood  than  usual.  To  meet  these  varying  demands,  the 
brain  has  the  power  of  regulating  the  heart  beat. 

Two  sets  of  nerves  pass  to  the  heart;  one  set  arises  in 
the    medulla   of    the   brain,    the   other   in   the  sympathetic 


/fearf , 


Fig.  77. — Diagram 

Showing  the  nerves  controlling  heart 
beat. 


THE    HEART   AND    THE    BLOOD    VESSELS  146 

nervous  system.  The  nerves  from  the  brain,  the  vagi  (Fig.  77), 
act  as  a  brake  on  the  heart;  if  they  are  artificially  stimulated, 
the  beat  of  the  heart  is  retarded;  or  if  they  are  severely 
irritated,  heart  action  may  stop  altogether  for  a  short  time, 
although  after  a  little  the  heart  escapes  from  its  influence  and 
goes  on  beating  again.  The  office,  then,  of  the  vagus  nerves 
is  to  keep  the  heart  from  beating  too  rapidly.  In  a  healthy 
body  they  would  never  stop  the  action  as  described  above, 
but  the  slowing  influence  is  necessary  when  the  body  tissues 
need  but  little  blood,  as  when  one  is  idle  or  asleep.  The 
vagus  nerves,  because  they  check  the  heart  action,  are  called 
the  inhibitor  nerves. 

The  second  pair  of  nerves  which  affect  the  heart  are  called 
the  sympathetic  nerves;  Fig.  77.  If  these  nerves  are  stimu- 
lated, they  make  the  heart  beat  faster  and  more  forcibly,  for 
which  reason  they  are  sometimes  called  the  accelerator  nerves. 

Thus  we  find  that  three  influences  are  constantly  affecting 
and  regulating  the  heart: 

1.  The  impulse  to  beat,  located  within  the  heart  itself. 

2.  The  inhibitory  influences,  which  reach  it  from  the  cen- 
tral nervous  system  over  the  vagus  nerves. 

3.  The  accelerator  influences,  which  come  over  fibres  by 
way  of  the  sympathetic  nerves. 

All  these  actions  take  place  unconsciously,  for  one  has  no 
power  voluntarily  to  modify  the  activity  of  the  heart.  If 
the  heart  is  thus  made  to  beat  more  or  less  rapidly,  it,  of 
course,  affects  the  rate  of  circulation.  The  more  rapidly  the 
heart  beats,  the  more  rapidly  the  blood  circulates,  and  a 
slowing  of  the  heart  beat  will  check  the  circulation  of  the  blood. 

THE  BLOOD  VESSELS 

All  vessels  in  the  body  which  conduct  blood,  ''pure"  or 
"impure,"  away  from  the  heart  are  called  arteries;  all  which 
carry  blood  to  or  toward  the  heart  are  called  veins.  Both 
wre  large  in  the  region  of  the  heart;  but  if  one  follows  the  ar- 


146 


ABVANCED  PHYSIOLOGY 


teries  away  from  the  heart,  he  finds  that  they  branch  re- 
peatedly until  at  the  ends  of  the  arms,  in  the  head,  skin  or 
(ntestine,  they  are  extremely  small.  The  smallest  subdivisions 
of  the  blood  vessels  are  called  capillaries.  Soon  these  minute 
, ,  ^      ...  tubes  unite  as  veins, 

Aorfa 


which  as  they  go  to- 
ward the  heart  are 
joined  by  others  and 
finally  are  even  larger 
than  the  arteries. 

The  Arteries. — 
From  the  right  ventri- 
cle, the  blood  enters 
the  pulmonary  artery ; 
Fig.  74.  This  artery 
divides,  sending  one 
branch  to  each  lung, 
and  inside  the  lungs 
each  branch  divides 
into  numerous  small- 
er branches;  finally, 
each  minute  twig 
breaks  up  into  a  pro- 
fusion of  lung  capil- 
laries. In  these  capil- 
laries the  blood  takes 
up  and  gives  off 
gases.  After  passing 
through  the  capilla- 
ries, the  blood  collects 
in  veins  which  unite 
to  form  large  trunks,  that  finally  leave  the  lungs,  going 
immediately  into  the  left  auricle;  Fig.  76.  From  here,  the 
blood  goes  to  the  left  ventricle,  and  thence  out  through 
an  artery,  the  aorta:  Fig.  76. 


Spleen 
'uperioritlesenhric 


Infesh 


Fig.  78.— Diagram 

Showing  the  aorta  and  its    chief  branches.     The 
broken  line  runs  through  the  middle  of  the  aorta. 


THE  HEART  AND  THE  BLOOD  VESSELS 


147 


Almost  before  this  aorta  emerges  from  the  base  of  the 

heart,  it  gives  off  two  small  arteries  which  supply  blood  to 

the  heart  muscle  itself.     It  may  seem  strange  that  the  heart 

with  the   great  stream  of  blood   flowing  through  it  needs 

special   arteries   to   supply   it   with   blood.     But   the   blood 

flowing  through  the  heart  does  not  nourish  it  any  more  than 

the  sap  running  up  the  tree  nourishes  the  outer  layers  of  the 

bark.    Hence  the  heart,  ]/gjp 

which  works  more  con-         .    ,  \  v 

Arferu  \s 

\ 


leucocyte 
(Erythrocyte 


stantlythan  any  other 
organ,  needs  its  own 
blood  supply,  which 
is  received  through 
these  coronary  arteries. 
The  aorta  goes  up- 
ward a  couple  of 
inches,  bends  toward 
the  left,  and  then  turns 
downward  through  the  Leucocifh 
thorax  and  abdomen, 
to  the  lower  part  of 
the  body,  as  shown  in 
Figure  78.  Before 
turning  downward  it 
gives  off  branches,  of 
which  the  carotids  pass 
to  the  head  on  each 
side  (Fig.  78);  while 
others,  the  subclavians, 
pass  to  each  arm,  thus  supplying  the  upper  extremities 
with  blood.  The  right  carotid  and  right  subclavian  leave 
the  aorta  as  one  trunk  that  soon  divides.  The  main  artery 
(aorta)  descends  through  the  abdomen,  side  branches  furnish 
blood  to  the  intestine  and  other  organs  in  the  abdomen,  and 
finally  the  aorta  divides,  one  braftch  extending  into  each  leg. 


Capillaries 

Fig.  79. — The  terminus  of  an  artbkt 

Showing  its  connection  with  a  vein  through  the 
capillaries.  In  the  upper  capillaries  are  shown 
blood  corpuscles  flowing  through  them.  Some 
leucocytes  are  shown  making  their  way  through 
the  capillary  walls,  and  others  quite  outside  of  the 
blood  vessels. 


148 


ADVANCED  PHYSIOLOGY 


The  chief  arteries  and  the  organs  to  which  they  go  are  diagram- 
matically  shown  in  Figure  78. 

The  Capillaries.^ — Each  artery  divides  and  sub-divides  into 
smaller   and  smaller  branches,  and   the   smallest  twigs   are 
distributed  to  the  tissues  in  every  part 
of  the  body.     If  we  follow  a  single  one 
of  these   branches,  we   find   that  each 
ultimate   twig  finally  breaks  up  into  a 
profusion  of  extremely  minute  vessels, 
the  capillaries,  too  small  to  be  seen  with 
the  naked  eye;  Fig.  79.     They  branch 
abundantly  and  unite  in  the  form  of  a 
network,  so  that  the  blood  which  flows 
into  them   has  no   definite  course  but. 
may   go  through  the  network  in   an; 
direction.     These  capillaries   (Fig.  80. 
are  of  great  importance,  for  it  is  througl 
them  that  the  blood  gives  up  its  nu- 
triment  to  the   tissues   and    takes    ii 
turn   the  waste  materials  which  ma^ 
have  collected  in  them. 

The   Veins. — After   passing   througl 
the  capillaries  the  blood  collects  in  ves- 
sels, called  veins.    The  smallest  of  these 
join  others  from  other  sets  of  capilla-| 
ries  until  they  soon  become  vessels  oi 
good  size.     Every  artery  ends  in  a  set 
of  capillaries,  and  each  set  of  capillaries 
empties  into  minute  veins  which  unite 
with  others  to  form  main  trunks,  carry- 
ing the  blood  back  toward  the  heart. 
The   blood   from   the   head   returns  in    two    large  veins  on 
each    side    of    the    neck,   known  as  the  jugular  veins  (Fig.j 
81),    and   these   join    the    large    veins    coming    from   eacl 
^See  Demonstration,  Appendix,  Section  14. 


Fig.  80. — Showing  the 
distribution  of  cap- 
illaries in  muscles 

The  black  irregular  lines 
are  the  capillaries.  Their 
minuteness  and  abundance 
may  be  inferred  from  the 
fact  that  the  muscle  fibres 
themselves  are  only  about 
one  five-hundredth  of  an 
inch  in  diameter. 


THE  HEART  AND  THE  BLOOD  VESSELS 


149 


arm    to    form    two    trunks,    wnich    finally    unite,    forming 
one   large   vessel,   the   superior   vena  cava; 


This 


Sub'^kj^tan 


?* 


WStomach 
\    5pleen 

\  Kidneif 


empties  directly  into 
the  top  of  the  right 
auricle,  as  we  have 
already  noticed.  The 
blood  from  the  lower 
part  of  the  body 
unites  in  large  veins, 
finally  forming  one 
great  trunk,  the  in- 
ferior vena  cava  (Figs. 
65  and  81),  which 
also  empties  into  the 
right  auricle.  By . 
these  two  large  veins 
all  of  the  blood  car- 
ried out  from  the  left 
ventricle,  after  pas- 
sing through  an  im- 
mense system  of  cap- 
illaries, is  brought 
back  to  the  right 
ventricle  to  be  sent 
once  more  to  the 
lungs.  In  general, 
one  may  say  that  the 
blood  vessels  near  the 
surface    of  the  body 

are  veins,  while  the  arteries  are  imbedded  deeply  in  the 
tistsue;  hence  the  wounding  of  the  flesh  is  almost  sure  to  cut  a 
vein,  but  will  not,  unless  very  deep,  injure  an  artery. 

I  As  a  rule  the  arteries  and  veins  going  to  and  from  a  given 
rea  or  organ  lie  closely  parallel  to  one  another,  and  often 
ave  the  same  names,  e.  g.  subclavian  artery,  subclavian  vein. 


/  Infesiine 


A  \M///ac 


Fig.    81. — Diagram 

Showing  the  course  of  the  chief  veins. 


160  ADVANCED    PHYSIOLOGY 

The  Portal  Blood  System. — The  portal  blood  system  has 
already  been  fully  described  (see  page  118).  Briefly  sum- 
marized, the  portal  vein  begins  in  the  capillaries  of  the  in- 
testine, stomach  and  spleen;  the  blood  from  all  these  organs 
runs  together  to  form  the  portal  vein  proper,  which  enters 
the  liver  and  there  breaks  up  into  capillaries,  for  purposes 
already  mentioned  (shown  also  in  Fig.  81).  The  liver,  then, 
receives  venous  blood  from  the  portal  vein,  and  arterial 
blood  from  a  branch  of  the  aorta  as  it  runs  down  through  the 
abdomen. 

GENERAL  SUMMARY  OF  THE  CIRCULATION 

The  circulation  of  the  blood  is  a  double  one,  one  half  going 
from  the  right  ventricle  through  the  lungs  and  back  to  the  left 
ventricle;  the  other  half  from  the  left  ventricle  through  the 
body  and  back  to  the  right  ventricle.     The  circulation  through, 
the  lungs  is  called  the  pulmonary  circulation;  that  through  the! 
rest  of  the  body  is  the  systemic  circulation.     During  its  entire] 
passage  around  the  body  the  blood  as  blood  never  leaves  the 
arteries,  capillaries  and  veins  (except  in  the  spleen) .   Remember- 
ing that  the  right  and  left  sides  of  the  heart  are  entirely  sepa-j 
rated,  it  is  plain  that  the  blood  after  leaving  the  left  ventricle] 
of  the  heart,  traverses  the  body,  returns  to  the  right  side  oi 
the  heart,  goes  thence  to  the  lungs  and  so  finally  returns  to] 
the  left  side  of  the  heart  whence  it  started.     It  has  however 
traversed  no  area  twice  even  though  it  has  been  twice  to  thej 
heart. 

STRUCTURE  OF  BLOOD  VESSELS 

If  an  artery  be  taken  from  an  animal's  body  it  will  be  found 
that  it  is  not  a  Ump  tube,  but  rigid  enough  to  keep  its  shape 
even  when  empty.  The  tissues  which  make  up  an  artery  are; 
arranged  in  three  chief  layers;  Fig.  82.     Next  to  the  cavity 


THE  HEART  AND  THE  BLOOD  VESSELS 


151 


of  the  tube  is  a  layer  of  thin,  flat  cells,  making  up  a  so-called 
lining  epithelium;  outside  this  is  a  middle  layer  of  involuntary, 
smooth  muscle,  the  fibres  of  which  pass  around  the  tube; 
the  outer  coating  is  made  of  connective  tissue  disposed  in  a 
dense,  spongy  mass  of  elastic  fibres  which  thus  gives  the  tube 
its  rigidity.  If  an  artery  is  stretched  it  will  return  to  its 
fiormal  length  like  a  strip  of  rubber;  if  it  is  closed  at  one  end 
and  air  forced  into  the  other,  the  artery  will  swell  to  two  or 
three  times  its  first  diameter. 


Epithelial  Lat/er 


■Coffnecfiv^isue  Latter 


i 


but  will  return  to  its  normal 
size  when  the  pressure  is 
relieved. 

Agents  commonly  causing 
the  contraction  and  relaxa- 
tion of  these  muscles  are  dis- 
cussed on  pages  162-163. 

Veins  are  made  of  the  same 
tissues  as  arteries ;  they  differ 
in  that  the  walls  are  very 
much  thinner  so  that  the 
tube  collapses  whenever  it  is 
empty.  The  muscle  and  con- 
nective tissue  coats  cannot  be 
easily  distinguished  as  their 
fibres  are  mixed  together,  and 
both  are  thin  as  compared 
with  the  same  layers  in  arteries;  Fig.  82  C.  Veins  are  much 
.jss  elastic  as  well  as  less  rigid  than  arteries.  Some  veins  are  also 
provided  with  valves  which  prevent  the  blood  from  flowing 
in  any  direction  except  toward  the  heart.  These  valves  are 
made  of  a  thin,  flexible  layer  of  connective  tissue  and  epithe- 
um  in  the  shape  of  half  cups,  fastened  to  the  walls  of  the 
veins  by  their  edges;  Fig.  83.  Thus  when  the  blood  flows 
in  one  direction  the  valves  flatten  against  the  side  of  the  tube 

(^  offer  very  Httl^  resistance;  bi^t  if  the  blood  st^xta  ba,clfr 


Fig.  82. — Showing  the  structure 
of  a  blood  vessel. 
At  A  is  shown  an  artery  with  the  different 
layers  removed  at  different  levels.  At 
B  is  a  cross  section  of  an  artery,  and  at 
C  of  a  vein.    (Modified  from  Landois.) 


152 


ADVANCED  PHYSIOLOGY 


ward  in  the  other  direction,  they  fill  and  thus  occupy  the 
whole  calibre  of  the  vein. 

Capillaries  are  delicate,  thin-walled  tubes  made  of  cells 
which  are  continuous  with  the  lining  epithelium  of  the  arteries 
and  veins;  Fig.  84.  The  capillaries  are  essentially  the  same 
as  the  arteries  with  the  muscle  and  connective  tissue  layers 
absent.  Through  their  thin  walls  the  fluids  of  the  blood 
easily  pass,  and  thus  come  in  contact  with  the  surround- 
ing tissues.  In  size,  capillaries  are,  on  the  average,  about  2X00 
of   an  inch  in  diameter,    and  their  numbers  are   countless. 

The  finest  needle  cannot 
pass  through  the  skin  with- 
out puncturing  some  of 
them,  and  the  deeper  lying 
organs  are  supplied  in  the 
same  way  as  those  on  the 
surface. 

Each  of  these  blood  tubes, 
then,  is  especially  fitted  to 
its  place  and  function;  the 
arteries  withstand  the  pow- 
erful, unremitting  driving 
of  blood  into  them  by  the 
heart;  the  capillaries  allow 
the  passage  of  the  nutrient 
fluids  and  gases  into  the 
surrounding  tissues,  and  also 
take  up  waste  fluids  and 
gases;  the  veins  conduct 
blood  back  to  the  heart, 
open  to  their  full  diameter 
all  the  time  to  permit  the 
easy  flow  of  blood,  yet  col- 
lapsible so  as  to  prevent  any  tendency  to  the  formation 
of  empty  spaces.     Of  course,  blood  will  not  tend  to  flow 


Fig.  83. — A  vlix  cut 

OPEN 

To  show  the  irregular  valves 

within. 


Fig.  84.— 

A  BIT  OF 
A  CAPIL- 
LARY 
Showing  it 
to  be  made 
of  a  single 
layer  of 
epithelial 
cells  only. 


THE    HEART   AND    THE    BLOOD    VESSELS  15S 

backward  through  the  arteries  since  the  heart  pump  is ,  con- 
stantly pushing  more  blood  along  into  them,  thus  keep- 
ing the  stream  in  one  direction.  Veins,  however,  which 
do  not  feci  this  impulse  from  the  heart,  are  provided  with 
valves  so  that  a  forward  flow  alone  is  possible. 

Diseases  of  the  Circulation. —  Anything  that  impairs  the 
circulation  will  evidently  interfere  with  normal  bodily  activity. 
Irregularities  in  the  action  of  the  valves  or  muscles  of  the  heart 
will  of  course  interfere  with  circulation.  Slight  imperfections 
in  heart  action  are  not  uncommon.  They  are  commonly  first 
noticed  by  a  shortness  of  breath  rather  than  any  trouble  around 
the  heart.  Persons  with  such  defects  must  live  a  more  quiet  life 
than  is  necessary  for  one  whose  heart  is  normal,  and  must  avoid 
all  forms  of  athletics  that  produce  excessive  strain  or  ex- 
haustion, e.g.  running  or  football.  With  care  in  regard  to  over- 
strain, these  heart  weaknesses  need  not  cause  especial  alarm, 
and  those  who  have  them  are  likely  to  live  as  long  and  useful 
lives  as  others  without  such  weakness. 

In  youth  all  the  arteries  are  strong  and  elastic  and  capable 
of  adapting  themselves  to  a  large  range  of  needs,  so  that  vigorous 
exercise,  even  of  long  distance  running,  is  well  endured.  When 
one  passes  middle  life,  however,  the  arteries  become  less  elastic 
and  less  able  to  respond  to  unusual  demands  upon  them.  When 
this  occurs  a  person  should  begin  to  live  a  more  quiet  life  and 
not  subject  his  heart  and  arteries  to  such  strains  as  would  come 
from  running  to  catch  a  train,  hurrying  up  stairs,  or  other 
vigorous  exercise.  Later  in  life  the  trouble  may  become  ex- 
cessive, producing  a  disease  called  hardening  of  the  arteries 
(arterial  sclerosis).  This  is  commonly  a  sign  of  the  approach  o^v 
old  age  and  for  it  there  is  no  known  remedy. 


CHAPTER  XI 

THE  CIRCULATION  OF  THE  BLOOD  AND  OF  THE 
LYMPH 

Nearly  every  one  has  seen  firemen  handling  hose,  and  has 
noticed  how,  as  the  engine  pumped,  water  spurted  out  at  the 
couplings  or  at  some  leak  in  the  hose,  showing  that  it  was 
under  great  pressure.     This  pressure  is  due  both  to  the  steady 

pumping   of  the  en- 
gine and  to  the  small 
nozzle  at  the  end  of 
the  hose.     If  the  noz- 
zle were  taken  off,  the 
water  would  run  in  a 
large    stream    but 
would  not  be  thrown 
any    great    distance, 
as    there    would    be 
nothing    to    prevent 
the  whole  pipeful  from  escaping  as  fast  as  the  water  was 
pumped  into  the  hose.     In  such  a  case  the  water  would  be 
under  little  or  no  pressure;  Fig.  85. 

BLOOD  PRESSURE  AND  ITS  CAUSE 

The  blood  in  our  arteries  is  under  pressure  for  similar  rea- 
sons, and  the  pressure  is  produced  by  two  similar  factors,  (1) 
the  heart  beat,  and  (2)  the  resistance  offered  by  the  capillaries 
to  onward  flow.  Since  the  heart  contracts  about  seventy 
times  a  minute  and  pushes  fresh  blood  into  the  aorta,  the 
influence  of  its  beat  is  evident.  The  narrower  arteries  and 
capillaries  offer  great  resistance   to   the   blood   flow,  corr§- 


Fig,  85, — Showing  the  effect  upon  pres- 
sure OF  DIFFERENT-SIZED  NOZZLES 
There  is  a  leak  in  each  hose  and  the  height  of  the 
stream  of  water  shows  the  pressure. 


Id 


CmcULATiON   01^   BLOOD   AND   OF   LYMPH 


Ut 


spending  roughly  to  the  nozzle  of  the  fireman's  hose.  When 
a  large  artery  is  wounded,  the  force  with  which  the  blood 
comes  from  the  cut  strikingly  shows  this  pressure. 

Naturally,  the  blood  in  all  persons  is  under  some  pressure  no 
matter  what  their  age.  Age  makes  much  difference,  however, 
and  it  has  been  found  that  in  boys  and  girls  of  ten  years  of  age 
the  pressure  is  only  about  one-half  what  it  is  at  twenty-five 
years  and  again  that,  in  persons  of  fifty,  it  is  about  eighteen  per 
cent  more  than  at  twenty-five.  Much  of  this  is  explained 
by  the  decreasing  elasticity  of  the  arteries  as  one  grows  older. 
In  the  aorta  near  the  heart  the  pressure  is  very  consider- 
able, but  it  is  slight  where  the  blood  flows  into  the  capillaries. 
It  will  be  remembered  that  the  cap- 
illary walls  are  very  thin,  only  the 
thickness  of  one  cell  for  the  most 
part;  and  this  condition,  which  is 
necessary  for  the  ready  exchange  of 
materials  through  their  walls,  would 
make  it  impossible  for  them  to 
resist  high  pressure. 

An  idea  of  the  amount  of  pressure 
in  the  arteries  has  sometimes  been 
gained  in  the  following  way.  If  a 
glass  U-tube  be  inserted  into  a  large 
artery  in  the  neck  (Fig.  86)  and  if 
this  tube  be  open  at  the  end,  the 
blood  will,  of  course,  flow  out  under 
its  pressure.     But  if   the   tube   be 

)laced  in   a  vertical    position    and 

lercury  be  put  into  it  to  hold  the 

>lood  back,  the  more  forcibly  the 

)lood  presses,  the  more  mercury  will 

)e  required  to  hold  it  back   and   keep   it  from  rising  and 

soming  out.     It  takes  about  nine  inches  of  mercury  in  the 

tube  to  prevent  the  blood  from  rising.     For  this  reason  we 


Fig.  86. — Showing  method 
of  measuring  blood 
pressure 

At  6  is  a  glass  tube  tied  within 
an  artery  of  some  animal ;  c,  a 
flexible  rubber  tube;d,  a  glass 
tube  containing  mercury.  The 
greater  height  of  the  mercury 
in  the  open  arm  of  the  tube 
shows  the  pressure. 


156  ADVANCED  PHYSIOLOGY 

say  that  the  pressure  of  blood  in  the  artery  is  nine  inches  of  mer- 
cury. The  pressure  varies  a  Httle  with  each  heart  beat,  being 
greatest  while  the  heart  is  contracting  and  least  when  the  heart 
is  resting.  The  pressure  decreases  as  the  arteries  become 
smaller  until  it  becomes  very  slight  in  the  capillaries.  This 
should  naturally  be  so,  for,  as  seen  on  page  152,  capillary  walls 
are  extremely  thin,  and  slight  pressm*e  would  rupture  them. 
That  they  possess  some  elasticity,  however,  is  evident  from  the 
appearance  of  the  face  when  blushing;  it  is  also  known  that 
the  lymph  passes  through  the  walls  of  capillaries,  sometimes 
rapidly,  sometimes  slowly,  and  this  seems  to  be  due  to  a  vary- 
ing pressure  within  them  as  well  as  to  a  varying  permeability 
of  capillary  walls. 

With  the  veins,  into  which  the  blood  flows  from  the  capil- 
laries, the  conditions  are  very  different.  They  are  wide  open 
where  they  end  at  the  heart,  so  that  there  is  nothing  to  keep  the 
blood  from  flowing  freely  imtil  it  reaches  that  organ.  There  is 
nothing  corresponding  to  the  nozzle  of  the  hose.  For  these 
reasons  the  blood  in  the  veins  is  under  much  less  pressm^e  than 
that  in  the  arteries,  and  varies  much  with  the  location  and  posi- 
tion of  the  organ. 

Bleeding  from  Arteries  and  Veins. — If  an  artery  is  cut,  the 
blood  will  come  out  in  forcible  jets,  and  prompt  action  is 
necessary  to  prevent  the  person  from  bleeding  to  death.  The 
bleeding  must  be  stopped  by  compressing  the  artery  between 
the  cut  and  the  heart.  Such  accidents  are  most  common  in 
the  legs  and  arms  where  they  can  easily  be  treated.  Figures 
87,  88  and  89  show  the  course  of  the  chief  arteries  in  an  arm 
and  leg.  The  easiest  and  most  effectual  way  to  stop  bleeding 
is  to  put  a  ligature  above  the  wound.  A  doctor  should  be 
summoned  and  the  ligature  kept  in  position  till  he  arrives. 

Wounds  in  veins  are  generally  less  serious  than  in  arteries, 
but  should  a  large  vein  be  cut  and  the  bleeding  be  so  rapid 
that  clotting  will  not  stop  it,  a  ligature  should  be  placed 
beyond  the  wound. 


CIRCULATION    OF    BLOOD    AND    OF    LYMPH 


157 


I 


The  Pulse. — In  an  earlier  section  the  real  cause  of  the  pulse, 
I.e.  the  constantly  alternating  increase  and  decrease  in  size 
of  the  arteries  due  to  heart  beat,  has  been 
noted.  There  is,  however,  no  pulse  in  the 
capillaries.  Such  a  constant 
stretching  and  swelling 
would  break  down  their  thin 
walls.  In  the  veins,  too, 
since  they  are  formed  by  the 
running  together  of  the  capil- 
laries, no  pulse  is  present. 
Two  agents  have  brought 
about  this  disappearance  of 
pulse  in  the  veins,  (1)  the 
elasticity  of  the  arterial 
walls,  and  (2)  the  opposi- 
tion which  the  small  arter- 
ies— arterioles — offer  to  on- 
ward blood  flow.  If  the 
arteries  had  rigid  walls,  there 
would  be  pulse  in  the  capil- 
laries and  veins,  in  spite  of 
the  small  calibre  of  the  arte- 
rioles; and  if  the  capillaries 
and  small  arteries  were  large, 
the  pulse  would  be  car- 
ried over  into  the  veins  in 
spite  of  the  elasticity  of  the  arterial  walls. 
We  may  note  here  also  that  the  pulse  is  not 
a  simple  throb,  but  consists  of  two  parts;  first, 
"beat,"  and  immediately  following,  a  second 
These  cannot  be  felt  as  separate  with  the 
aked  finger,  but  are  detected  with  a  pulse  recording  apparatus. 
The  first  part  of  the  pulse  wave  is  calused  by  the  sudden  rush  of 
lood  into  the  arteries  when  the  ventricle  contracts,  while  the 


Fig.    87.— The 
abm   from   in 

FRONT 

Showing  the  chief 
arteries.  (Modi- 
fied from  Tiede- 
mann) 


Fig.  88.— The 
thigh  and 
knee  from 
the  inside 

Showing  arteries. 
(Modified  from 
Tiedemann) 


strong,  abrupt 
'weaker  beat." 


158 


ADVANCED    PHYSIOLOGY 


% 


less  prominent  beat  is  supposed  to  be  caused  by  the  closure  of 
the  semilunar  valves  of  the  heart. 

RATE  OF  BLOOD  FLOW 

With  such  a  powerful  organ  as  the  heart 
driving  the  blood  about  the  body,  the  blood 
current  is  fairly  swift.  The  blood  flows  rapidly 
in  the  large  arteries,  but  as  they  branch,  the 
total  area 'of  arteries  becomes  greater,  so  that 
it  flows  more  and  more  slowly;  just  as  a  river 
flows  swiftly  through  a  narrow  gorge,  but 
more  slowly  when  it  spreads  out  into  a 
broad  stream.  In  the  large  arteries  near 
the  heart  blood  flows  at  the  rate  of  about 
sixteen  inches  per  second.  Farther  from 
the  heart  the  rate  is  about  nine  inches  per 
second;  in  the  smaller  arteries  it  is  much 
slower;  in  the  capillaries  it  flows  not  more 
than  -^\y  inch  per  second.  After  passing  into 
the  veins  the  rate  increases  and  as  the  veins 
merge  into  trunks  and  finally  reach  the 
heart  it  is  about  as  rapid  as  in  the  arteries 
that  leave  the  heart.  It  is  in  the  capillaries 
that  the  blood  exchanges  new  food  materials 
for  worn-out  matter,  and  oxygen  for  carbon 
dioxid;  and  to  allow  this  to  take  place  to  ad- 
vantage a  very  slow  flow  is  necessary.  The 
length  of  time  required  for  the  blood  to  make 
a  complete  circuit  of  the  body  is  calculated  at 
twenty-eight  seconds,  requiring  thirty-two  to 
thirty-four  heart  beats. 

THE  VASO-MOTOR  SYSTEM 
Regulation  of  the  Size  of  the  Blood  Vessels.— 
By  changing  the  rapidity  of  the  heart  beat,  the  whole  body 
may  be  made  to  receive  more  or  less  blood  than  usual;  but 


Fig.  89.— The 
lower  leg 

FROM  BE- 
HIND 

Showing  arter- 
ies. Many  of 
the  muscles 
have  been 
removed  . 
(Modified 
from  Tiede- 
mann) 


CIRCULATION   OF   BLOOD   AND    OF   LYMPH  159 

there  is  another  method  of  modifying  the  amount  of  blood 
received  by  the  separate  organs.  If  the  only  method  of 
increasing  the  amount  of  blood  sent  to  any  organ  were 
by  accelerating  the  rate  of  the  heart  beat,  thus  increasing  the 
circulation  all  over  the  body,  it  would  be  as  inconvenient  as 
if  the  only  way  of  regulating  the  gas  in  a  house  were  by 
turning  it  on  or  off  at  the  gas  factory.  The  body  is 
therefore,  supplied  with  a  more  elaborate  system  so  that 
at  any  moment  any  single  organ  may  receive  a  greater 
or  less  supply  of  blood  than  usual. 

All  the  small  arteries,  as  well  as  the  large  ones,  are  en- 
circled by  muscles  (Fig.  82),  whose  contraction  causes  a  dimi- 
nution in  the  size  of  the  blood  vessels.  If  the  muscles  relax,  the 
artery  will  become  larger  because  of  the  pressure  of  the  con- 
tained blood.  The  capillaries  also  contract  and  expand  in  a 
similar  way.  Certain  parts  of  the  brain  and  spinal  cord  are 
connected  by  nerves  with  all  of  these  muscles  and  thus  con- 
trol their  size.  These  nerves  are  called  the  vaso-motor  nerves, 
and  the  muscles,  the  vaso-motor  muscles.  The  muscles  and 
nerves,  together  with  their  nerve  centers  in  the  brain  and 
spinal   cord,  constitute  the  vaso-motor  system. 

Two  sets  of  vaso-motor  nerves  are  connected  with  the  blood 
vessels;  one  of  them  tends  to  constrict  the  vessels,  and  the 
nerves  composing  it  are  called  the  vaso-constrictor  nerves. 
This  set  is  acting  all  the  time,  keeping  most  of  the  vessels 
sUghtly  tightened;  not  sufficiently  to  shut  off  the  flow  of  blood 
but  enough  to  prevent  them  from  becoming  loose  and  flabby; 
this  set  supplies  especially  the  vessels  of  the  skin  and  intes- 
tine. The  other  set  of  vaso-motor  nerves  causes  the  vessels  to 
enlarge;  they  are  called  the  vaso-dilator  nerves  and  arc  found 
especially  supplying  vessels  of  the  muscles  and  glands. 

Action  of  the  Vaso-Motor  System. — A  few  examples  of  the 
work  of  this  system  may  make  its  functions  clearer.  W3 
often  hear  people  say  that  one  should  not  take  severe  or 
rapid  exercise  soon  after  eating.     Why  is  this  so?     3ecft\«6^» 


160 


ADVANCED    PHYSIOLOGY 


when  the  muscles  of  the  arms  or  legs  are  working  they  need 
more  blood  than  usual.  Hence  the  vaso-motor  nerves  cause 
the  blood  vessels  of  the  muscles  to  relax  and  thus  allow  more 
blood  to  be  supplied  to  them.     The  consequence  is  that  less 

blood  is  at  liberty  to 
go  to  the  cells  in  the 
stomach  and  intes- 
tinal walls,  when 
these  should  be  busi- 
ly secreting  diges- 
tive juices  or  passing 
along  the  food  by 
peristaltic  contrac- 
tions. Thus,  witn 
too  little  blood  to 
effect  digestion  the 
food  is  sluggishly 
handled,  secretions 
are  less  in  amount 
than  they  need  be, 
and  the  food  is  not 
sufficiently  changed 
to  allow  of  read} 
absorption. 

Blushing    and 
turning  pale  are  evi- 
dences of  the  work 
of  this  system.     These  changes  are  due  entirely  to  the  differ- 
ence in  the  size  of  the  blood  vessels  of  the  face  and  are 
brought  about  through  the  influence  of  nerves;  Fig.  90. 

Control  of  the  Vaso-Motor  System. — These  messages  to  the 
blood  vessels  go  out  from  the  brain  without  any  consciousness 
on  our  part,  however;  in  fact  we  cannot  control  them,  as  is 
shown  by  the  vain  struggles  of  people  to  keep  from  blushing 
^hoD  they  are  embarrassed.    This  is  a  most  fortunate  pro- 


Fig.    90. — Apparatus   for    demonstrating 
the  function  of  the  vaso-motor  system 

The  arm  is  placed  in  the  glass  cylinder  which  is  filled 
ip-ith  water.  The  tube  a  connects  with  the  cyl- 
inder also.  Evidently  any  swelling  of  the  arm  will 
cause  the  level  of  the  water  in  the  tube  to  rise. 
Having  noted,  by  the  marker,  the  height  of  the 
water,  the  person  whose  arm  is  in  the  cylinder  is  set 
to  studying  hard.  The  marker  quickly  falls,  show- 
ing that  blood  has  left  his  arm  to  go  to  the  aid  of 
the  hard  working  brain.  If  he  stops  studying  the 
marker  rises  again.  (Fick) 


CIRCULATION    OF    BLOOD    AND    OF    LYMPH  161 

vision,  too;  for  the  different  organs  of  the  body  need  different 
amounts  of  blood  at  different  times,  and  if  this  blood  supply 
were  dependent  on  our  conscious  regulation  of  it,  we  could 
accomplish  very  little  else,  and  even  that  function  would  be 
imperfectly  performed. 

The  dilator  influences,  however,  do  not  arise  in  the  same 
place  as  do  the  constrictor;  the  nerves  which  carry  messages 
causing  constriction  of  blood  vessels  rise  in  the  medulla,  or 
hind  brain.  From  there  they  go  down  the  spinal  cord,  and 
are  thence  distributed  in  various  directions.  The  vaso-con- 
strictor  center,  therefore,  is  in  the  medulla,  or  hind  portion  of 
the  brain.  No  definite  place  can  be  determined,  however,  as 
the  centre  from  which  messages  go  out  to  cause  vessels  to  en- 
large. Some  fibres  apparently  arise  in  the  vaso-constrictor 
center,  while  others  do  not. 

IMPORTANCE  OF  A  VIGOROUS  CIRCULATION 

We  seldom  realize  the  fact  that  the  whole  body  is  traversed 
in  every  direction  by  arteries,  veins  and  capillaries  and  that 
blood,  a  living  stream  under  considerable  pressure,  is  running 
through  it  every  minute  of  our  fives. 

A  swift  brook,  dashing  down  a  steep  hifi,  takes  along  with 
it  everything  but  the  large  pebbles  and  stones;  all  the  loose 
mud  and  dirt  are  carried  along,  and  are  left  behind  only  when 
the  stream  becomes  sluggish  and  slow.  Then  the  materials 
in  the  muddy  water  catch  on  the  grass  and  sticks  in  the  stream, 
and  everything  under  the  water  is  covered  with  dirt  and  refuse. 
So  when  the  blood  flows  strongly  and  steadily,  it  can  pick  up 
many  of  the  wastes  of  the  body  and  carry  them  away.  This, 
however,  is  not  due  solely  to  the  swiftness  of  .the  stream,  but 
because,  by  means  of  this  rapid  flow,  more  blood  is  brought  to 
and  carried  away  from  every  spot  in  the  body;  and  the  more 
blood  there  is  coming  into  contact  with  any  tissue,  the  more 
effectually  that  tissue  is  fed  and  the  more  perfectly  it  is 
cleansed  of  its  waste  debris.     In  the  business  world  there  is 


162  ADVANCED   PHYSIOLOGY 

usually  a  supply  of  those  things  for  which  there  is  a  demand: 
just  so  here,  the  ''law  of  supply  and  demand"  is  constantly 
holding  true;  blood  will  flow  rapidly  and  vigorously  whenever 
one  does  things  which  demand  a  plentiful  flow.  Vice  versa, 
a  sluggish  flow  is  the  rule  where  the  habits  of  the  person  are 
sluggish. 

This  is  the  reason  for  the  bracing  effect  produced  through 
the  stimulation  of  the  skin  by  rubbing,  as  after  a  bath;  for 
this  affects  surface  capillaries,  and  their  walls  relax.  The 
inrush  of  blood  reacts  on  all  the  contributing  arteries,  and  a 
readjustment  of  many  vessels  takes  place,  rousing  them 
from  their  inert  condition.  In  the  same  way  the  skin  is  stimu- 
lated by  fresh  air,  with  its  accompanying  changes  of  tempera- 
ture, which  produce  a  response  in  the  vaso-motor  system 
creating  a  mild,  though  extensive  effect  on  the  whole  body. 
One  single  pursuit,  one  single  kind  of  activity,  mental  or 
physical,  makes  the  supply  and  demand  one-sided.  Diver- 
sity of  exercise  and  interest  is  necessary  to  secure  "a  sound 
mind  in  a  sound  body,"  an  indispensable  requisite,  if  one  is 
to  meet  life  with  thrill  and  enthusiasm.  Exercise,  either  in 
work  or  recreation,  produces  a  demand  for  new  materials,  for 
fresh  blood.  Change  in  one's  train  of  thought,  as  in  con- 
genial, lively  conversation,  upsets  the  listlessness  of  the  nerve 
centers,  affects  the  rate  of  blood  flow,  and  tones  up  the  whole 
system. 

The  Influence  of  Heat  and  Cold  upon  Circulation. — Changes 
in  temperature  cause  great  modification  in  the  activities  of  all 
organs  in  the  body.  As  a  rule  all  living  tissues  work  with 
greater  readiness  when  warm  than  when  cold.  The  influence 
of  heat  is  especially  noticed  in  its  effect  on  the  blood  vessels 
in  the  skin;  when  the  body  is  warm  the  walls  of  the  arteries  in 
some  areas  relax  more  than  usual,  the  capillaries  become 
over-full  and  one  is  said  to  be  "flushed  with  heat." 

On  the  other  hand  cold  causes  blood  vessels  to  contract, 
and  all  the  muscles  to  act  slowly.     The  first  effect  of  going 


CIRCULATION   OF   BLOOD   AND   OF   LYMPH  163 

out  into  the  cold  air  may  be  a  whitening  of  the  skin;  but  later 
an  expansion  of  the  capillaries  causes  the  skin  to  become 
flushed.  The  expansion  and  contraction  of  these  vessels  ex- 
plain our  feelings  of  warmth  and  cold.  The  blood  in  the  interior 
of  the  body  is  considerably  warmer  than  that  on  the  surface. 
Since  the  nerve  endings  which  perceive  sensations  of  heat  are 
located  in  the  skin,  and  not  in  the  inside  of  the  body,  one  has 
no  sensation  of  heat  so  long  as  the  warm  blood  is  in  the  in- 
ternal organs.  But  if  the  body  is  exceptionally  warm,  from 
vigorous  exercise,  for  example,  the  blood  vessels  in  the  skin 
relax  for  the  purpose  of  allowing  the  hot  blood  to  flow  more 
rapidly  through  the  skin,  that  it  may  be  cooled  off.  This 
extra  rush  of  warm  blood  to  the  skin  produces  a  sensation  of 
heat.  In  other  words,  the  feeling  of  warmth  which  one  has 
on  a  warm  day  or  after  exercising,  is  simply  a  sign  that  the 
body  is  cooling  off  as  rapidly  as  possible.  On  the  other  hand, 
on  a  cool  day,  the  body  wishes  to  retain  its  heat,  and  the 
blood  vessels  in  the  skin  are  consequently  constricted.  The 
skin  feels  cold  because  there  is  so  little  warm  blood  flowing 
through  it.  Thus  the  feeling  of  warmth  does  not  necessarily 
mean  that  the  body  is  hotter  than  usual,  but  only  that  the 
arterioles  in  the  skin  are  relaxed  and  that  warm  blood  is 
flowing  rapidly  through  them.  If  the  skin  is  flushed,  one 
foels  warm  even  though  he  is  losing  heat  and  so  actually  be- 
coming colder. 

Fainting. — The  common  and  very  unpleasant  experience 
of  fainting  is  due  to  a  smaller  supply  of  blood  than  usual  in 
the  brain.  This  condition  may  be  brought  about  by  many 
causes,  e.g.  by  the  lack  of  a  sufficient  amount  of  oxygen  in  the 
air,  by  the  presence  of  a  disagreeable  odor,  or  by  some  dis- 
order in  the  digestive  functions.  The  last  named  cause  is  the 
most  frequent.  In  such  cases  the  action  of  the  heart  may  be 
slower  than  usual  or  the  vessels  in  the  brain  may  contract  so 
that  it  is  insufficiently  supplied  with  blood.  This  causes  a 
^.topping  of  its  regular  activities,  and  the  person  becomes  un- 


164  ADVANCED    PHYSIOLOGY 

conscious.  If  he  can  be  placed  flat  on  his  back  with  the  head 
lower,  if  possible,  than  the  rest  of  the  body,  blood  will  run 
into  the  brain  again,  and  the  person  regain  consciousness. 
While  a  fainting  person  may  seem  to  need  immediate  attention 
and  help,  the  common  tendency  for  everyone  who  is  near 
to  rush  to  his  relief  is  unfortunate.  There  is  usually  no 
especial  danger,  and  if  two  or  three  are  waiting  on  the 
patient  others  may  much  better  remain  quietly  away,  and 
thus  not  prevent  free  circulation  of  air,  about  the  patient, 
who  will  doubtless  very  quickly  recover. 

The  Effect  of  Drugs  upon  the  Circulation. — The  whole  cir- 
culation may  be  more  or  less  profoundly  modified  by  various 
drugs,  some  of  which  increase  and  others  decrease  its  action. 
Caffein,  for  example,  the  active  principle  in  coffee  causes  the 
heart  to  beat  more  forcibly  and  at  the  same  time  causes  a  con- 
striction of  the  small  arteries  so  as  to  raise  blood  pressure.  J 
For  this  reason  it  is  called  a  stimulant.  " 

It  has  been  frequently  stated  that  alcohol  increases  the 
activity  of  the  heart.  Careful  experiment,  however,  shows 
that  not  only  is  its  effect  not  that  of  a  stimulant,  but  that 
when  used  in  large  amounts  it  very  markedly  weakens  the 
action  of  the  heart.  If  taken  in  small  amounts  only,  the 
heart  sometimes  shows  a  slight  increase  in  its  rate  of  beating, 
but  this  occurs  only  when  the  brain  becomes  excited,  and  if 
the  person  is  kept  quiet  no  change  in  the  heart  beat  is  notice- 
able. Its  primary  action  is  thus  on  the  brain,  as  we  shall 
find  later. 

A  second  effect  of  alcohol  is  more  evident.  The  small 
blood  vessels  in  the  skin  are  enlarged,  probably  from  the 
partial  paralysis  of  the  vaso-motor  center.  This  produces 
a  flushed  skin,  a  feeling  of  warmth  and  a  false  feeling  of 
increased  circulation.  Its  result  is  to  send  more  blood  through 
the  skin  with  a  consequent  extra  loss  of  heat.  This  action  is 
evidently  not  due  to  stimulation  but  to  the  relaxation  of  the 
muscles  and  is  thus  a  decrease  of  activity  rather  than  an  in- 


CIRCULATION    OF    BLOOD    AND    OF    LYMPH 


165 


crease,  even  though  the  blood  does  flow  a  little  more  rapidly 
through  the  skin.  These  facts  make  it  clear  that  alcohol  can- 
not properly  be  called  a  stimulant  of  the  circulatory  organs. 

THE  LYMPH  SYSTEM 

Source  of  Lymph. — Blood  in  its  usual  condition  occurs 
only  in  blood  vessels,  and  so  long  as  it  is  in  the  vessels  the 
innumerable  living  cells  of  the  body  cannot  profit  by  the 
nourishment  it  contains.  But  while  it  is  passing  through  the 
capillaries,  the  liquid  plasma,  together  with  some  of  the  white 

/fflmph 
//I'i     Vessel 


y^W 


Arfeno< 


Capillartf 

Fig.    91. — Diagram 

showing  the  origin  of  the  lymph  and  the  interchange  of  material  between  the  living 
cells  and  the  lymph.  Oxygen,  various  food  materials,  and  water  pass  from  the 
capillaries  to  the  cells  via  the  lymph.  The  cells  give  up,  e.  g.  carbon  dioxid, 
uric  waste  and  water,  which  is  carried  away  either  through  the  veins  or  through  the 
lymph  vessels. 

but  with  none  of  the  red  corpuscles,  oozes  out  through  the 
thin  walls  of  these  vessels.  Outside  (see  arrows  in  Fig.  91), 
this  plasma  flows  irregularly  in  all  directions  among  the  liv- 
ing parts  of  the  body,  actually  bathing  the  cells.  It  is  no 
longer  known  as  blood  but  as  lymph  and  soon  collects  in 
small  vessels  called  lymph  vessels;  Fig.  92.  This  lymph  is 
a  clear,  watery  fluid,  containing  in  solution  all  of  the  food 


166 


ADVANCED  PHYSIOLOGY 


Arifni       ,i^>5^^/ 


Fig.  92. — Diagram 

Showing  the  beginning  of  the  lymph  vessels 
and  their  relation  to  the  capillaries. 


materials    which    have    entered   the    blood,    and   the   body 
cells  take  their  nourishment  from  it.     Moreover,  the  waste 

products  which  arise  in 
the  body  are  ejected  from 
the  cells  directly  into  the 
same  lymph.  The  lymph, 
therefore,  serves  both  to 
supply  the  cells  with  their 
nourishment,  and  to  re- 
ceive their  waste  pro- 
ducts. It  is  thus  an  ex- 
tremely complicated  solu- 
tion, containing  all  the 
material  which  the  body 
absorbs,  and  all  the  excre- 
tions which  the  body 
produces. 
Flow  of  the  Lymph. — We  may  obtain  a  better  idea  of  the 
flow  of  the  lymph  and  of  the  lymphatic  vessels,  by  making  a 
comparison.  Suppose  a  gravel  walk  extends  from  the  top 
to  the  bottom  of  a  hillside.  At  the  time  of  a  heavy  rainfall 
all  the  pebbles  in  the  walk  will  be  bathed  in  the  water  that 
runs  over  them.  Let  these  pebbles  correspond  to  the  cells  in 
the  extremities  of  the  body,  bathed  in  lymph.  As  we  go 
down  the  hill  a  little  distance,  we  notice  the  water  running 
together  in  little  shallow  streams;  no  definite  channels  of  any 
depth  will  be  formed,  perhaps,  but  there  will  be  little  rills  in 
which  the  water  runs.  These  correspond  to  the  beginnings 
of  lymph  ducts  not  as  yet  definitely  walled  in. 

As  we  go  farther  on  down  the  hill,  we  find  streams  of  con- 
siderable size  made  by  the  flowing  together  of  the  small  rills. 
These  larger  streams  flow  in  very  definite  channels,  and  there 
are  banks  on  each  side  whicn  keep  the  water  in  one  route. 
These  definite  streams  may  correspond  to  the  larger  lymph 
ducts,  with  walls  of  their  oviu.     All  along  the  course  of  these 


CIRCULATION    OF    BLOOD    AND    OF    LYMPH 


167 


Lym'ph 
glands 


larger  streams,  both  on  and  away  from  its  banks,  the  pebbles 
continue  to  be  wet  with  the  rain,  and  the 
tiny  rills  flow  constantly  to  join  the  larger 
current,  until,  at  the  foot  of  the  hill,  there 
will  be,  perhaps,  a  single  large  stream  car- 
rying all  the  water  that  has  fallen  in  the 
path. 

In  a  similar  way  the  lymph  collects,  at 
first  in  indefinite  channels  without  walls, 
but  farther  on  in  tubes  with  walls,  which 
are  then  called  lymph  vessels.  Figure  92 
shows  the  way  in  which  these  lymph  ves- 
sels originate,  and  Figure  93,  which  shows 
their  numbers  in  the  superficial  tissues  of  the 
arm,  only  exemplifies  the  abundance  with 
which  all  parts  of  the  body  are  supplied. 

What  Becomes  of  the  Lymph? — Lymph 
is  primarily  the  liquid  part  of  the  blood 
squeezed  out  of  the  capillaries.  It  must  go 
somewhere,  for  if  it  continued  to  accumu- 
late, it  would  form  pool-like  masses  among 
the  tissues.  Sometimes  lymph  does  gather 
in  certain  spaces;  e.g.  the  trouble  called 
water  on  the  knee  is  caused  by  the  accumu- 
lation of  lymph  in  that  joint  as  the  result 
of  an  injury.  Severe  rubbing  at  any  point 
in  the  skin  causes  lymph  to  collect  and 
form  a  blister.  A  large  gathering  of  lymph 
produces  the  disease  called  dropsy.  Ordina- 
rily, however,  lymph  flows  away  as  fast  as  it 
appears. 

The  lymph  vessels  coming  from  all  parts 
of  the  body  finally  unite  into  two  large 
trunks.  Lymph  from  the  lower  part  of 
the  body  flows  into  the  large  thoracic  duct  (Figs.  65  and  94)  j 


Fig.  93.  —  Ths 
lymph  vessels 
in  the  superfi- 
cial tissues  of 

THE  ARM 


168 


ADVANCED  PHYSIOLOGY 


Ric/MLt/mpi 
duci- 


^.^  Vessel  sum 
■"^       Head 


which,  as  we  have  already  noticed,  receives  the  lymph  trom  the 
intestine  and  consequently  the  fat  absorbed  into  the  lacteals. 

It  is  also  joined  by 
subordinate  vessels 
from  the  left  side  of 
the  head  and  left  arm, 
and  then  empties  into 
the  left  sub-clavian 
vein  in  the  shoulder 
region;  Fig.  94.  The 
lymph  from  the  right 
arm  and  right  side  of 
the  head  flow  together 
into  a  smaller  vessel 
which  empties  into 
the  right  sub-clavian 
vein.  Thus  the  lymph, 
which  originally  came 
from  the  blood,  after  | 
flowing  through  the 
system  of  lymph 
tubes,  gets  back  again  i 
into  the  blood,  pro- 
ducing a  continuous 
circulation  of  lymph 
from  the  blood  to  the 
living  cells  and  back 
again  to  the  blood. 
Lymph  transfers  the 
nutriment  directly  to  the  living  cells  and  then  brings  back  to 
the  blood  the  excreted  products  which  are  then  carried  to  certain 
organs  for  elimination. 


.Thoracic 
ducf 


Li^mph 
cflands 


OF     THE 


Fig.    94. — Showing    the    course 

thoracic  duct 

Its  entrance  into    the  vein  in  the  neck  and  also  the 

right  lymphatic  duct. 


DUCTLESS  GLANDS 


In  different  parts  of  the  body  are  a  number  of  organs,  some- 


CIRCULATION    OF    BLOOD    AND    OF    LYMPH 


169 


Due  /       Secrefmq  Cells 


times  called  ductless  glands,which  do  not  seem  to  belong  to  any 
of  the  general  systems.  Since  one  type  of  these  is  associated 
with  the  lymph  system,  all  of  them  will  be  mentioned  here. 

A  gland  (Fig.  95)  is  a  collection  of  cells,  the  protoplasm 
of  which  takes  from  the  blood  more  fluid  than  is  used  in  the 
cell  itself,  and  changes  it  chem- 
ically, after  which  the  extra 
amount  is  secreted,  or  shed  into 
some  cavity,  (as  the  pericardial 
cavity  for  example) ,  or  into  some 
narrow  passage  or  duct  (as  for 
instance,  those  of  the  salivary 
glands).  There  are,  however, 
some  glands  in  the  body  which 
do  not  empty  their  secretions 
into  any  duct  or  cavity;  they  are 
plentifully  supplied  with  blood 
vessels,  and  so  have  much  ma- 
terial at  hand  from  which  to 
make  quantities  of  a  special  kind 
of  secretion.  Whatever  fluid  they 
make  is  poured  directly  into  the 
blood  vessels  and  the  substances  they  furnish  are  called 
hormones. 

Lymph  Glands. — The  first  of  these  ductless  organs  are  the 
so-called  lymph  glands.  These  are  small,  more  or  less  round 
masses  of  tissue,  scattered  along  the  course  of  the  lymph 
vessels;  Fig.  93.  They  are  found  in  many  parts  of  the  body, 
particularly  at  such  places  as  the  shoulder  and  hip  joints. 
At  present  practically  nothing  is  known  of  their  functions, 
although  it  is  believed  that  they  are  the  seat  of  white  blood 
corpuscle  formation. 

The  Spleen. — The  spleen  is  located  near  the  lower  wall  of 
the  stomach  and  is  supported  there  by  folds  of  the  mesentery; 
Fig.  78,  page  146.     So  plentiful  is  its  blood  supply  that  when 


^em 


Arfert^ 

95. —  Diagram 
simple  gland 

Showing  the  secreting  cells  and  the 


Fig. 


OF 


blood  vessels  supplying  them. 


170  ADVANCED    PHYSIOLOGY 

seen  in  the  living  animal  it  shows  distinct  shrinking  and  en- 
largement in  size  with  each  beat  of  the  heart.  The  size  of  the 
organ,  too,  would  lead  one  to  think  that  it  must  be  of  con- 
siderable importance.  In  many  animals  it  is  as  long  as  the 
stomach  itself,  though  not  so  broad.  The  use  of  the  spleen  is 
not  known.  It  can  be  entirely  removed  from  the  body  without 
fatal  results.  Various  suggestions  have  been  made  as  to  its 
functions;  some  think  it  concerned  with  the  making  of  new 
red  blood  corpuscles,  while  others  take  the  opposite  view, 
that  it  is  a  place  where  old  ^'.orpuscles  are  destroyed. 

The  Thyroid  Glands. — The  thyroid  glands  are  located,  one 
lobe  on  each  side  of  the  oesophagus,  a  little  below  ''Adam's 
apple,'*  or  the  voice  box  of  the  trachea  ;  see  Fig.  98,  page  178. 
Their  influence  on  the  living  processes  in  the  body  is  much 
more  evident  than  that  of  the  spleen.  The  material  which 
they  pour  into  the  blood  has  a  very  definite  effect  upon  the 
manner  in  which  the  blood  nourishes  different  parts  of  the 
body.  If  a  person  is  born  lacking  these  glands,  there  is, 
apparently,  a  case  of  badly  regulated  nutrition;  the  child 
grows  up  with  a  stupid  brain,  weak  Hmbs  and  a  misshapen 
body — a  condition  called  cretinism.  If  such  a  child  is  given 
a  medicine  containing  the  extract  of  the  thyroid  glands  of 
some  animal,  the  trouble  is  frequently  removed,  the  body 
recovering  its  shape,  and  a  normal  development  resulting. 
The  enlargement  and  disease  of  the  thyroid  glands  sometimes 
appears  as  great  swellings  on  the  neck,  a  trouble  known  as 
goitre. 

Adrenal  Bodies. — Just  above  each  kidney  is  located  a  small 
gland,  about  the  size  of  a  walnut,  called  an  adrenal  body. 
These  bodies,  too,  empty  their  secretion  into  the  blood  as 
it  passes  through  them.  While  the  amount  of  their  secre- 
tion in  a  given  time  is  small,  the  fluid  contributed  is  very 
potent.  Its  main  effect  is  to  influence  the  muscles  in  the 
walis  of  the  arteries  so  that  they  contract  and  lessen  the  cali- 
bre of  the  vessels.     Under  normal,  healthy  conditions,  the 


CIRCULATION    OF   BLOOD  AND   OF   LYMPH  171 

amount  of  this  secretion  is  probably  just  enough  to  cause  the 
walls  of  the  arteries  to  maintain  a  certain  amount  of  contrac- 
tion, thus  preventing  them  from  being  too  lax. 

Other  Ductless  Glands. —  There  are  several  other  ductless 
glands,  one  connected  with  the  thyroid  called  the  parathyroid ; 
one  connected  with  the  brain,  pituitary  body.  The  pancreas 
also,  besides  furnishing  digestive  juices  to  the  intestines  through 
its  duct,  gives  other  important  substances  to  the  body  through 
the  blood.  The  exact  and  entire  function  of  these  ductless 
glands  is  not  fully  understood. 

One  must  not  presume,  however,  that  these  glandular  organs 
just  mentioned  are  the  only  ones  which  pass  into  the  blood 
as  it  goes  through  them  substances  which  are  essentially 
hormones  in  character.  Probably  it  is  safe  to  say  that  every 
tissue  in  the  body  makes  its  cordrihution  and  in  this  way  sends 
material  to  every  other  tissue,  definitely  influencing  it  in  one 
way  or  another. 

In  healthy  then,  each  tissue  gives  out  its  own  hormone  in  such 
quantity  and  of  such  quality  that  all  other  tissues  are  benefited 
by  it.  This  fact  should  come  to  us  as  a  suggestion  that,  by 
careful  eating,  breathing,  sleeping,  and  exercise,  each  tissue  is 
kept  strong  and  healthy  and  so  contributes  to  the  strength  and 
health  of  the  whole  body. 


CHAPTER  XII 
THE  RESPIRATORY  ORGANS 

The  daily  distribution  of  food  materials  in  a  city  seems 
a  wonderful  accomplishment;  delivery  of  milk  and  eggs,  for 
example,  from  thousands  of  farms  to,  perhaps,  a  million 
inhabitants,  scattered  in  thousands  of  houses,  apartments 
and  flats  is  made  at  least  every  twenty-four  hours.  In  the 
body,  however,  there  are  more  than  a  million  times  as  many 
cells  as  there  are  people  in  any  city  on  earth;  yet  each  cell  re- 
ceives its  food  much  more  often  than  once  a  day. 

Besides  food,  another  substance  is  delivered  to  the  body 
cells  by  the  blood;  this  is  oxygen. 

THE  FUNCTION  OF  RESPIRATION 

No  living  thing,  animal  or  plant  (except  a  few  bacteria)  can 
subsist  without  it.  Unicellular  and  many  other  lower  organ- 
isms absorb  it  directly  through  the  body  surface;  others  (in- 
sects) are  provided  with  branching  tubes  which  lead  air  from 
the  exterior  to  the  internal  cells;  while  others  have  special 
breathing  organs,  such  as  lungs  or  gills,  from  which  oxygen  is 
absorbed  by  the  blood. 

To  understand  why  we  need  oxygen  we  have  only  to  return 
to  the  comparison  of  the  body  to  a  furnace.  If  all  the  dampers 
in  a  stove  are  closed,  the  fire  burns  slowly,  or  else  goes  out.  If 
all  the  cracks  and  joints  in  the  stove  could  be  closed  air-tight, 
the  fire  would  never  burn.  If  the  drafts  are  opened  and  air  let 
in,  the  fire  burns  rapidly.  It  is  the  union  of  the  wood  or  coal 
with  oxygen  which  results  in  its  ''burning,''  and  giving  off  heat. 

Of  course  there  is  no  flame  in  the  body;  the  food  materials 
inside  it  never  glow  like  coals,  but  they  do  combine  with 
oxygen  and  give  off  heat,  very  slowly  it  may  be,  but  none  the 
less  certainly.     The  process  is  essentially  the  same  as  that 

172 


THE  RESPIRATORY  ORGANS 


173 


which  takes  place  in  the  burning  or  oxidizing  of  fuel  in  a  stove. 
If  all  air  (oxygen)  were  kept  from  entering  the  blood,  i.e.  if 
the  dampers  were  shut,  the  foods,  even  though  digested  and 
in  the  blood,  could  not  be  oxidized,  and  would  be  only  so  much 
dead  weight  and  of  no  value.  The  stove  is  connected  with  a 
chimney  to  carry  off  the  smoke  and  other  gases  that  are 
formed  in  the  burning  fuel.  Gases  are  also  formed  in  the  body 
by  the  oxidizing  of  foods,  and  these  Ukewise  must  be  passed  off. 
The  body  needs  to  exchange  gases  with  the  air.  Respiration 
is  the  process  of  gas  exchange  in  the  tissues  of  living  things. 

THE  NOSE  AND  PHARYNX 

Figure  40  shows  the  structure  of  the  nasal  passages.  Air 
enters  by  the  two  nostrils  into  the  nasal  chambers,  or  canals 
which  are  separated  from  one  another  by  a  partition  made  of 
cartilage  and  connective  tissue  in  front,  and  strengthened 
farther  back  by  a  thin  vertical  sheet  of  bone.  The  canals 
pass  back  through  the  nose,  just  above  the  hard  palate,  and 
enter  the  upper  por- 


Olfaclvrtf 
Nerve 


Jurbma^ed^cjz 
Bones 


£usfacman 
Tube 


tion  of  the  pharynx 
by  separate  openings. 
The  bony  and  car- 
tilaginous partition 
between  the  two  nasal 
canals  presents  a  fairly 
smooth  surface;  but 
the  opposite  wall  of 
each  canal  has,  pro- 
jecting into  it,  a  much 
folded,  wrinkled, 
spongy  arrangement 
of  thin  bones,  the  tur- 
binated bones;  Fig.  96. 
The  walls  of  the  nose  cavities  are  covered  with  a  smooth 
epithelium  which  contains  innumerable  mucous  gland  cells. 


Tongue 


FMe 

Fig.  96. — Vertical  section  through  the 

NOSE 
Showing  the  turbinated   bonea  and  the  olfactory 
nerve  entering  from  the  brain  into  the  upper  nasal 

passages. 


174 


ADVANCED    PHYSIOLOGY 


These  keep  the  membranes  always  moist,  even  though  the 
air  which  is  constantly  going  back  and  forth  through  the 
nose  would  tend  to  dry  them.  In  addition  to  the  gland 
cells  of  the  nasal  membranes,  there  are,  mingled  with  them  in 
the  deeper  parts  of  the  canals,  many  ciliated  cells,  whose 
cilia  are  in  constant  motion,  causing  a  current  in  the  mucous 
fluids.  The  turbinated  bones  might  seem  to  be  actual  ob- 
structions in  the  nasal  passages,  but  they  really  serve  a 
double  purpose. 

1.  They  so  fill  up  the  passages  that  very  coarse  materials 
taken  in  with  the  air  are  strained  out  by  them,  but  a  far 
more  effectual  cleansing  is  obtained  because  the  canals  run- 
ning between  these  bones  are  so  crooked.  Particles  inhaled 
through  them  lodge  and  stick  on  their  moist  surfaces,  so  that 
they  may  be  driven  away  by  the  cilia,  which  beat  about  in 
such  a  way  that  they  gradually  push  along  any  dust  which 
touches  them,  until  it  is  driven  from  the  air  passages  into  the 
throat,  where  it  is  swallowed  with  the  saliva  or  expelled  from 
the  mouth.  In  this  way  the  dust  particles  of  the  air  are 
prevented,  to  a  considerable  extent,  from  reaching  the  lungs. 

2.  During  cold  weather,  the  position  of  the  turbinated  bones 
in  the  nose  passages  and  the  warmth  of  the  membranes  which 
cover  them  make  them  serve,  almost  precisely,  the  purpose  of 
a  radiator.  Just  as  air  forced  over  steam  pipes  is  warmed, 
so  air  breathed  through  the  meshes  of  the  turbinated  bones  is 
warmed    and  thus  does  not  chill  the  delicate  lung  passages. 

These  facts  explain,  in  part,  the  injury  that  may  result 
from  mouth  breathing.  When  the  mouth  is  open,  air  rushes 
rapidly  into  the  throat  and  lungs,  carrying  dust  particles 
along  with  it.  Moreover,  such  air  is  not  properly  warmed 
and  is  taken  into  the  lungs  too  cold.  These  two  things  make 
a  person  more  liable  to  diseases  of  the  throat  and  lungs,  and 
because  of  the  close  connection  between  the  ears  and  the 
throat,  sometimes  produce  deafness.  For  the  benefit  of  his 
future  health,  every  young  person  should  notice  carefully 


THE  RESPIRATORY  ORGANS  175 

how  he  breathes.  The  pernicious  habit  of  breathing  through 
the  mouth  is  easily  overcome,  either  by  a  Uttie  care,  or  with 
the  aid  of  a  surgeon;  see  page  177. 

Lachrymal  Canals. — Everyone  has  noticed  that  when  tears 
are  running  freely,  they  somehow  get  into  the  nose,  whence 
they  may  run  out  of  the  nostrils,  but  more  often  they  pass 
hack  to  the  throat  and  are  swallowed  (a  child  is  seen  swallow- 
ing frequently  when  crying  hard).  Two  tiny,  ciliated  canals 
leave  the  inner  corner  of  each  eye  and  carry  the  tears  to  the 
tear  sac,  which  is  located  very  near  the  eye  in  the  tissues  of 
the  nose.  From  each  tear  sac  a  canal,  about  three-quarters 
of  an  inch  long,  passes  down  to  open  into  the  nose  chamber 
of  that  side  where  the  secretion  is  ordinarily  discharged. 

The  Sense  of  Smell. — The  sense  of  smell  is  extremely  deli- 
cate. Whatever  the  something  is  which  passes  from  an 
object  to  the  cells  lining  the  nose,  it  must  be  exceedingly 
minute,  otherwise  the  object  giving  off  the  odor  would  entirely 
waste  away  in  a  very  short  time.  Perfectly  dry  substances, 
such  as  balsam  needles  and  sachet  powders,  give  out  fragrance 
for  years  and  yet  do  not  lose  appreciably  in  weight.  If  a 
bottle  of  peppermint  oil  be  opened  for  a  few  minutes,  its  odor 
will  fill  a  house,  and  yet  if  weighed  in  delicate  scales,  no  ap- 
preciable amount  will  be  found  to  have  disappeared  from  the 
bottle. 

The  upper  passages  in  the  nose,  where  the  olfactory  sense 
is  located,  are  separated  from  the  brain  by  a  very  thin  par- 
tition, the  ethmoid  bone.  This  bone  is  perforated  by  numer- 
ous short  canals,  through  which  olfactory  nerves  pass  directly 
from  the  front  end  of  the  brain.  As  soon  as  they  enter  the 
nose  they  subdivide  into  numerous  fine  fibres  which  end 
among  the  olfactory  cells,  both  on  the  middle  partition  and  on 
the  upper  and  middle  turbinated  surfaces;  Fig.  96. 

The  main  passages  through  which  air  is  drawn  in  ordinary 
l)reathing  lie  in  the  lower  part  of  the  nose  and  go  nearly 
straight  back  from  the  nostrils   to   the   openings  into   the 


176 


ADVANCED  PHYSIOLOGY 


Nerrehfhe 
"Brain 


pharynx,  or  throat.  The  main  current  of  air  does  not  enter 
the  spaces  high  up  in  the  nose,  between  and  somewhat  below 
the  level  of  the  eyes,  yet  it  is  the  lining  of  these  upper  passages 
that  is  especially  constructed  for  smelling.  The  two  chief 
kinds  of  cells  in  this  lining  are:  mucous  cells,  which  are  cylin- 
drical and  rather  large,  and 
the  true  olfactory  cells,  which 
are  slender  and  rod-like;  Fig. 
97. 

Just  what  happens  to  the 
olfactory  cells  when  scented 
air  enters  the  nose,  is  not 
known;  but  in  some  way  they 
are  irritated  and  hand  over 
to  nerve  fibres  connected  with 
them  a  message  which  is  car- 
ried to  the  brain;  and  this 
message  produces  a  sense  of 
smell. 

The  olfactory  area  is  too 
high  in  the  nose  for  the  main 
currents  of  air  to  pass  over 
it.  Consequently,  when  one 
wishes  to  perceive  very  faint  odors,  the  muscles  of  the  nose 
contract  sUghtly,  widening  the  passages,  and  one  ''sniffs"  the 
air.  By  this  we  mean  that  one  draws  in  the  air  in  short, 
quick  breaths,  which  dislodge  the  air  already  in  the  smelling 
region,  and  fill  it  with  a  new  supply.  These  movements  of 
the  nose  and  the  sniffing  process  are  seen  most  plainly  in 
animals,  like  dogs  or  foxes,  which  use  this  sense  in  locating 
food. 

Adenoid  Growths. — Adenoids  are  unusual  growths  just 
back  of  the  nasal  canals,  in  the  region  where  these  open 
into  the  pharynx.  Occasionally  they  occur  as  far  down 
as  the  tonsils,  in  which  case  the  tonsils,  too,  are  generally  in- 


Celli  lininq iht[\  .„  ,  „r  |,fv,rj.    „  _  „ 

ror(/Ce//s 

Fig.  97. — The  nerves  and  cells 
connected  with  the  sense  of 

SMELL 

The  olfactory  and  mucous  cells  are  on  the 
surface  of  the  nasal  passages,  the  rest  of 
the  cells  and  fibres  being  within  the 
other  soft  tissues  in  the  nose.    (Schafer) 


THE   RESPIRATORY  ORGANS  177 

fiamed.  They  usually  take  the  form  of  small  bunches,  vary- 
ing from  the  size  of  a  pea  to  that  of  an  almond.  Sometimes 
they  are  stalked,  and  have  the  appearance  of  tiny  mushroom- 
like elevations.  They  occur  most  frequently  in  children 
between  the  ages  of  ten  and  fifteen  years,  and  are,  apparently, 
not  induced  by  any  particular  exposure.  They  are  growths 
of  useless  tissue,  sometimes  rather  tough  and  wart-Uke,  but 
more  serious  than  warts,  because  they  grow  in  the  delicate 
breathing  passages.  Their  presence  may  make  breathing 
through  the  nose  difficult  and  so  induce  mouth  breathing. 
They  may  impair  hearing  by  closing  the  passages  into  the 
ears  and  they  prevent  the  perfect  development  of  the  whole 
body.  They  should  always  be  removed  before  they  become 
numerous.  The  operation  is  a  simple  one,  easily  performed 
by  a  skilful  surgeon.  If  one  finds  his  nose  constantly  ''stopped 
up  "  so  that  he  cannot  breath  through  it  easily,  he  should  have 
it  examined  by  a  physician  to  see  if  the  trouble  is  due  to 
adenoids. 

THE  TRACHEA 

After  passing  through  the  nose  and  reaching  the  pharynx, 
air  is  drawn  to  the  lungs  through  the  windpipe  or  trachea, 
beginning  with  the  enlarged  portion,  the  larynx;  Fig.  98. 
The  trachea  is  about  five  inches  long  and  three-fourths  of 
an  inch  in  diameter.  It  leaves  the  pharynx  cavity  just  back 
of  the  tongue;  the  opening  into  it,  the  glottis,  is  covered  by  a 
lid  called  the  epiglottis,  made  of  connective  tissue  and  muscle, 
supported  on  a  framework  of  cartilage;  Fig.  40.  During 
ordinary  breathing  it  is  raised,  leaving  a  free,  open  passage 
for  the  entrance  of  air.  When  food  is  swallowed,  it  closes 
down  over  the  glottis,  preventing  particles  from  "  going  the 
wrong  way."  If,  by  chance,  a  bit  of  food  passes  by  it  into 
the  windpipe,  a  violent  spasm  of  coughing  takes  place.  The 
trachea  is  held  open  by  a  number  of  cartilaginous  rings  in  its 
walls,  so  that  the  air  may  pass  freely  through  it;   Fig.   98. 


178 


ADVANCED  PHYSIOLOGY 


Larunx 


These  rings  are  not  complete  but  are  in  the  form  of  irregular 
horseshoes  with  the  open  part  behind,  where  the  windpipe 
comes  next  to  the  oesophagus.      The  windpipe  is,  therefore, 

soft  and  flexible  next  to  the 
oesphagus  so  that  the  swal- 
lowing of  food  through  the 
latter  is  not  hindered.  As 
long  as  the  larynx  is  open 
and  the  epiglottis  is  raised, 
air  drawn  in  either  through 
the  nostrils  or  the  mouth 
passes  with  perfect  freedom 
down  the  windpipe  into  the 
lungs. 


THE  LUNGS 

Where  the  lower  end  of 
the  trachea  enters  the  tho- 
rax, it  divides  into  right  and 
left  bronchial  tubes  which 
immediately  enter  the  lungs. 
Each  lung  is  an  elongated, 
elastic  bag  of  spongy  tissue 
and  completely  fills  one  half 
of  the  thoracic  cavity,  if 
we  leave  out  of  account  the 
part  occupied  by  the  heart 
and  large  blood  vessels.  The  shapes  of  the  lungs  cannot  be 
easily  described,  since  each  fits  closely  about  the  bordering 
structures,  the  heart,  the  walls  of  the  cavity  and  the  dia- 
phragm below.  The  right  lung  is  a  little  larger,  though  shorter, 
than  the  left;  Fig.  73.  The  lungs  are  divided  into  lobes,  aUke 
in  construction;  the  right  lung  has  three  and  the  left  two 
lobes,  each  lung  thus  being  a  compound  structure. 


Bronchioles  ■ 


Lun^ 


Fig.   98. — The  trachea  and  lungs 

Showing  the  air  passages.  The  position  of 
the  thyroid  glands  is  shown  in  dotted 
lines.     (Modified  from  Sappey) 


THE    RESPIRATORY   ORGANS 


179 


Air  Passages  in  the  Lungs. — In  the  lungs  each  bronchial 
tube,  or  bronchus,  divides  into  smaller  branches,  called  bron- 
chioles, and  these  divide,  until  finally  they  become  minute 
twigs,  as  shown  in  Figure  98.  At  the  end  of  every  twig,  the 
air  passage  is  swollen  into  a  chamber,  or  series  of  chambers, 
somewhat  larger  than  the 
passage  itself.  These  little 
air  spaces  are  known  as 
alveoli,  and  each  is  partially 
.subdivided  into  smaller 
compartments,  ''air-sacs'' 
or  ''air-cells."  There  are 
thousands  of  them  in  each 
hmg,  and  they  are  the 
places  where  blood  and  air 
exchange  gases.  This  con- 
struction provides  a  very 
large  amount  of  surface,  it 
being  estimated  that  the 
area  so  provided  amounts 
to  about  960  square  feet; 
this  is  over  one  hundred 
times  the  skin  surface  of  the 
body.  The  walls  of  the  alveoH  are  very  thin  and  elastic,  so  that 
they  are  expanded  when  filled  with  air,  and  would  become 
shrunken  and  nearly  collapsed  if  emptied. 

In  spite  of  the  filtering  that  the  air  receives  in  its  passage 
through  the  nose,  much  fine  dust  is  constantly  passing  into 
the  windpipe  and  lungs.  This  would  produce  trouble  were 
there  no  means  for  its  removal;  but  the  whole  series  of  pas- 
sages, the  trachea  and  all  the  bronchioles  in  the  lungs,  are 
lined  with  the  tiny,  waving,  hair-like  bodies  we  have  called 
cilia;  Fig.  3  d.  These  cilia  are  in  constant  motion,  creatiiij^ 
a  current  upward  toward  the  pharynx,  and  any  dust  taken  in 
with  the  air  and  caught  on  the  moist  surfaces  is  carried  up- 


Vesieb 


Fig 


99. Two    OF     THE    AIR     SACS    IN 

THE  LUNGS 
Highly  magnified.     The  black  lines  are  sec- 
tions of   the  capillaries  that  fill  the  walls  of 
the  air  sacs.     The  arrows  show  the  direc- 
tion of  the  exchange  of  gas. 


180  ADVANCED  PHYSIOLOGY 

ward  toward  the  throat,  to  be  finally  expelled  from  the  mouth 
in  the  sputum,  or  to  be  swallowed.  When  working  or  riding 
where  it  is  very  dusty,  although  one  may  have  cleared  the 
throat  of  what  mucus,  sahva,  or  dust  has  collected  there, 
after  waiting  for  a  time  he  finds  on  clearing  the  throat  again, 
that  more  dust  has  accumulated.  A  service  which  can  hardly 
be  overestimated  is  thus  performed  for  us  by  these  minute 
ciliary  projections  from  the  cells  in  the  air  passages. 

Blood  Vessels  in  the  Lungs. — A  second  set  of  passages  in 
the  lungs  is  that  of  the  blood  vessels.  We  have  already 
noticed  that  the  pulmonary  artery  from  the  right  ventricle 
divides,  sending  a  branch  into  each  lung.  Each  of  these 
branches  separates  in  the  lungs  into  smaller  and  smaller 
divisions.  These  minute  vessels  finally  break  up  into  ex- 
tremely complex  sets  of  capillary  vessels  in  the  walls  of  the 
alveoli;  Fig.  99.  The  walls  of  these  air  sacs,  as  well  as  those 
of  the  blood  vessels,  are  extremely  thin  and  the  blood,  flow- 
ing in  the  capillaries,  is  brought  into  very  close  relation  with 
the  air.  There  is,  of  course,  no  actual  contact,  for  the  blood 
remains  in  the  blood  vessels  and  the  air  in  the  alveoli;  but 
the  membranes  that  separate  them  are  extremely  thin,  so 
thin  indeed,  that  they  do  not  form  any  hindrance  to  gaseous 
exchange  between  the  air  and  the  blood  in  the  alveoli.  In 
other  words,  the  gases  in  the  alveoli  pass  with  perfect 
readiness  into  the  blood,  and  gases  that  are  dissolved  in  the 
blood  can  with  equal  ease  pass  out  of  the  vessels  into  th( 
alveoU.  It  is  while  the  blood  is  flowing  through  the  capillaries] 
in  the  walls  of  these  alveoli  that  changes,  which  constitute] 
an  important  part  of  the  process  of  respiration,  take  place. 

The  Pleura. — On  the  outside  of  the  lungs  is  a  double  fol( 
of  membrane  called  the  pleura;  Fig.  73,  page  136.     To  under- 
stand its  relations,  imagine  a  large,  thin,  flexible  bag,  com- 
pletely closed  at  its  top  and  bottom,  to  be  wrapped  around! 
the  lungs.     One  side  of  the  bag  would  thus  be  in  contact  with 


THE    RESPIRATORY    ORGANS  181 

the  lungs  and  the  other  side  with  the  walls  of  the  thorax. 
Between  the  two  would  be  the  space  that  really  is  the  cavity 
of  the  bag.  When  the  lungs  move,  these  two  layers  of  the  sac 
glide  over  each  other.  The  layers  themselves  are  made  of 
glandular  cells  which  secrete  a  clear,  watery  liquid  into  the 
space  between  them,  keeping  their  surfaces  moist  and  mak- 
ing it  possible  for  the  lungs  to  move  without  friction  or  irrita- 
tion. 

DISEASES  OF  THE  RESPIRATORY  ORGANS 

Colds. — The  commonest  ailment  of  the  respiratory  organs 
is  what  is  called  a  cold.  This  is  primarily  an  inflammation  of 
the  mucous  membrane  of  the  nose  and  throat.  By  the  term 
inflammation  is  meant  an  enlargement  of  the  capillary  blood 
vessels,  causing  too  abundant  a  supply  of  blood  in  the  region 
in  question  and  bringing  about  a  variety  of  other  undesirable 
effects,  such  as  great  sensitiveness,  pain  and,  perhaps,  fever. 
In  an  ordinary  cold  the  mucous  membrane  is  very  sensitive, 
secretes  an  abundance  of  mucus  and  becomes  swollen.  This 
state  of  things  may  interfere  with  the  free  passage  of  air, 
since  the  nostrils  may  be  so  closed  by  the  swollen  membranes 
that  one  can  breathe  only  through  the  mouth.  Soaking  the 
feet  in  hot  water  and  drinking  hot  lemonade  will  sometimes 
prevent  the  development  of  a  cold  and  is  usually  effective 
in  the  initial  stages.  • 

Taking  Cold. — Perhaps  there  is  no  way  of  avoiding  colds 
entirely,  but  it  is  possible  to  reduce  their  frequency.  Oddly 
enough,  the  method  which  most  people  adopt  to  prevent  colds 
frequently  results  in  making  them  more,  rather  than  less 
susceptible  to  this  ailment.  To  understand  this  seeming 
paradox,  we  should  find  out  first,  what  causes  lead  up  to 
a  cold.  The  actual  cause  of  colds  is  not  known  though  they  are 
perhaps  due  to  bacteria.  It  is  quite  certain  that  they  are  not 
induced  simply  by  exposure  to  cold,  as  the  name  would  lead 
one  to  believe,  but  are  associated  with  the  imperfect  control 


1S2  ADVANCED   PHYSIOLOGY 

exercised  by  the  vaso-motor  system  over  the  small  blood 
vessels  of  the  skin.  Persons  who  live  an  out-of-door  life, 
although  frequently  exposed  to  extremely  cold  weather,  rarely 
suffer  from  colds.  Those  who  regularly  take  cold  baths,  thereby 
giving  their  skin  repeated  stimulation,  are  almost  immune 
against  colds. 

One  is  almost  certain  to  take  cold  if  he  dresses  very 
warmly,  never  goes  out  without  heavy  wraps,  bundles  the  neck 
with  a  fur  collar,  or  turns  up  the  coat  collar  around  the  ears 
when  out  of  doors  and,  when  in  doors,  lives  in  very  warm 
rooms.  Such  a  method  of  caring  for  one's  self  will  seldom 
fail  to  bring  on  colds.  The  vaso-motor  system  of  the  skin 
demands  exercise  just  as  much  as  the  muscles  of  the  legs  or 
arms.  If  we  fail  to  use  our  muscles,  they  lose  the  power  of 
acting  vigorously.  So  too,  if  we  fail  to  give  the  vaso-motor 
muscles  their  exercise,  they  become  sluggish.  If  we  should 
wear  less  clothing,  the  skin  would  constantly  be  more  or  less 
under  the  influence  of  the  ever-changing  temperature  of  the 
air,  so  that  the  blood  vessels  would  be  kept  vigorous  and 
active.  We  might  then  frequently  feel  cold,  but  we  should 
not  "  take  cold." 

As  soon  as  one  finds  himself  showing  a  tendency  to  colds, 
he  should  begin  at  once  to  invigorate  the  skin  by  proper  stimuli 
and  thus  to  tone  up  the  vaso-motor  system.  A  cold  bath  is 
the  best  means  of  doing  this,  and  if  a  person  when  young 
accustoms  himself  to  bathing  every  morning  in  cold  water, 
he  will  soon  find  himself  almost  proof  against  colds;  see  page 
162.  Especially  is  it  necessary  that  the  neck  should  be  stimu- 
lated by  cold  water,  and  not  wrapped  in  furs,  for  this  seems 
to  be  the  part  of  the  body  where  there  is  the  greatest  trouble. 

Colds  in  themselves  are  of  comparatively  little  importance, 
but  they  sometimes  lead  to  more  serious  troubles.  The  in- 
flammation which  starts  in  the  nose,  as  e.g.  in  a  head  cold, 
may  pass  into  the  throat,  and  then  down  the  trachea  into  the 
lungs.    A  cold  in  the  lungs  or  the  chest  is  liable  to  produce 


THE    RESPIRATORY    ORGANS  183 

more  trouble  than  one  in  the  head.      When  serious  inflani' 
mation  attacks  the  lungs,  however,  we  no  longer  call  it  a  cold. 

Bronchitis. — Inflammation  in  the  bronchi  or  their  subdivi- 
sions in  the  lungs  is  called  bronchitis.  It  is  really  Uttle  more 
than  a  cold  which  has  reached  the  smaller  air  passages  of  the 
respiratory  organs,  but  it  produces  much  trouble  there;  for 
many  of  the  tubes  are  small  and  any  inflammation  or  secretion 
fills  them  more  easily  and  quickly  than  the  same  amount  would 
the  larger  passages  of  the  nose.  In  the  case  of  a  little  child 
or  an  old  person  bronchitis  may  cause  severe  illness,  or  even 
death;  but  with  those  of  middle  age  it  is  not  much  more 
serious  than  a  severe  cold,  although  it  produces  more  dis- 
comfort and  more  distressing  symptoms  and  is  more  lasting. 

Pneumonia. — If  the  inflammation  extends  still  farther  into 
the  lungs,  it  is  liable  to  develop  into  a  far  more  serious  disease, 
called  pneumonia.  While  this  is  a  germ  disease,  and  cannot 
therefore  be  originated  by  a  cold,  a  cold  often  prepares  the 
lungs  for  the  ready  implantation  of  the  pneu- 
monia bacteria.  These  bacteria  are  common  in  ($  £}'«y 
the  mouth  and  throat   (Fig.  100  a),  but  if  the  •"•^ 

lungs   are  healthy,  the  germs  may  be  inhaled  '^//\* 

without  harm.   When,  however,  the  tiny  air  sacs     h    ;v'^"\^"» 
in  the  lungs  are  inflamed  by  a  cold,  their  sur-  'V'J^ft^ 

faces  offer  a  place  where  these  pneumonia  germs  „  .^^  __ 
can  get  a  foothold.  Developing  there,  they  may  ^^g  g^^j 
soon  produce  violent  inflammation  accompanied  teria  op 
by  high  fever.  Secretions  accumulate  in  the  air  pneumonia 
sacs,  filling  them  partially  or  wholly,  so  that  ^'  thebac- 
portions  of  the  lungs  may  become  practically 

.  r>  J  f  J  TUBERCU- 

soUd  and  breathing  sometimes  be  difficult.      Of      losis 
course,  if  all  the  air  sacs  were  thus  filled,  death 
would  at  once  result;  but  it  generally  happens  that  only  cer- 
tain places  in  the  lungs  are  affected.     After  a  time,  if  the 
trouble  is  not  too  severe,  the  liquid  mass  in  the  lungs  begins 
-x)  be  absorbed,  and  eventually  the  lungs  may  clear  up  en- 


184  ADVANCED    PHYSIOLOGY 

tirely  and  complete  recovery  take  place.  After  recovery,  how- 
ever, the  person  may  have  a  second  attack,  for  this  disease, 
unlike  such  diseases  as  scarlet  fever  and  measles,  does  not 
render  a  person  less  susceptible  to  its  return. 

Pneumonia  is  one  of  the  most  dangerous  of  diseases  and  in 
some  localities  more  people  die  from  the  effects  of  it  than 
of  any  other  common  disease.  There  is  no  household  remedy 
which  is  especially  beneficial  in  a  case  of  pneumonia,  and 
every  patient  should  be  promptly  placed  in  the  hands  of  a 
physician.  Every  precaution  should  be  taken  to  avoid  the 
trouble,  and  the  best  way  to  prevent  it  is  to  guard  against 
colds. 

Tuberculosis. — There  is  another  little  germ  which  may 
seize  the  occasion  of  a  cold  to  attack  a  person.  It  is  called 
the  tvibercle  bacillus  (Fig.  100  h)  and  is  one  of  man's  most  deadly 
foes.  It  may  enter  the  body  in  any  of  several  ways,  but  its 
chief  method  of  entrance  is  through  the  mouth  with  food,  or 
through  the  nose  with  the  air.  We  sometimes  hear  it  said  that 
a  person  had  a  cold  which  developed  into  consumption.  When 
we  remember  that  consumption  is  caused  by  a  definite  germ 
and  that  a  cold  is  something  quite  different,  it  is  evident 
that  a  cold  cannot  turn  into  consumption  any  more  than  a 
worm  can  turn  into  a  snake.  But  a  cold  in  the  lungs  inflames 
all  the  air  passages  and  these,  when  inflamed,  are  much  more 
easily  infected  by  bacteria  than  when  in  healthy  condition. 
If  one  is  in  good  health,  the  tuberculosis  bacilli  may  frequently 
be  inhaled  without  harming  him.  But  if  the  walls  of  the 
air  passages  are  weakened  in  any  way,  the  germs  may  find  a 
chance  for  growth. 

This  microscopic  foe  is  far  more  dangerous  than  any  of  our 
larger  enemies.  After  it  has  once  entered  the  body,  i+  may 
pass  to  almost  any  part  of  it  and,  stopping  there,  produce 
trouble.  It  sometimes  lodges  in  the  abdomen  and  produces 
serious  and  fatal  diseases  of  the  digestive  organs.  Sometimes 
it  grows  in  the  skin,  producing  an  ugly  trouble,  called  lupus* 


THE  RESPIRATORY  ORGANS  I8f 

Sometimes  it  is  in  the  glands  of  the  skin,  causing  them  to  swell 
and  thus  producing  scrofula.  It  grows  in  the  kidneys,  caus- 
ing nephritis,  or  in  the  brain,  occasioning  some  forms  of 
meningitis.  It  brings  about  joint  troubles,  one  of  which  is 
hip  disease.  But  the  most  common  trouble,  and  the  most 
serious  of  all,  results  when  it  attacks  the  lungs  and  brings  on 
consumption.  Here  it  produces  nodules,  or  tubercles  (hence 
the  name,  tuberculosis),  causing  the  lung  tissue  to  degenerate, 
sometimes  to  the  extent  of  breaking  through  into  the  blood 
vessels,  and  producing  bleeding  in  the  lungs,  or  hemorrhages, 
as  they  are  called.  Oftentimes  these  diseased  places  heal, 
leaving  the  lungs  more  or  less  solid  in  the  placed  where  the 
germs  have  been  working.  But  if  the  disease  progresses  suffi- 
ciently, the  person  becomes  more  and  more  poisoned  by  the 
germs,  the  lungs  become  more  and  more  impaired  in  their 
functions,  until  death  occurs.  In  most  communities  this 
disease  causes  more  deaths  than  any  other.  In  some, 
pneumonia  causes  a  higher  death  rate. 

The  War  against  Tuberculosis. — For  centuries  mankind 
has  known  of  this  disease  and  has  been  helpless  before  it. 
Its  cause  was  not  known,  no  cure  had  been  discovered,  and 
nothing  could  be  done  to  check  its  ravages.  But  in  the 
last  thirty  years  great  advances  have  been  made,  and  to-day 
we  are  armed  with  many  means  of  fighting  it.  We  have 
learned  that  not  all  persons  who  contract  the  disease  die, 
as  was  formerly  supposed.  It  has  lately  been  shown  that 
most  persons  who  have  reached  adult  life  have  at  some  time 
had  an  attack  of  this  disease  and  have  recovered  without 
even  knowing  that  they  had  had  it.  In  such  cases  the  attack 
probably  appeared  as  a  cold,  which  persisted  for  a  time,  but 
finally  disappeared.  This  shows  that  even  when  the  germ 
gets  into  the  body,  the  body  has  strong  powers  of  resisting 
and  overcoming  it.  When  the  trouble  is  discovered  at  the 
outset,  the  chances  for  recovery  are  good,  if  the  person  at- 
tacked will  live  out  of  doors,  where  he  may  breathe  fresh  air 


186  ADVANCED    PHYSIOLOGY 

night  and  day,  winter  and  summer.  The  sanatoria,  where 
consumptives  are  taken,  rely  for  their  cures  upon  Ufe  in  the 
fresh  air  and  good  food,  and  their  patients  are  kept  out  of 
doors  even  in  cold  winter  weather.  No  medicine  has  as  yet 
been  found  that  is  of  any  use,  despite  the  many  advertisements 
with  such  claims. 

The  recent  advance  in  the  treatment  of  tuberculosis  has 
been  not  so  much  in  curing  as  in  preventing  the  disease.  We 
know  enough  to-day  of  the  means  of  its  distribution  to  stop  it, 
if  we  could  only  induce  everyone  to  act  intelligently  in  the 
matter.  The  best  way  to  fight  it  is  to  distribute  information 
concerning  it,  as  a  wide-spread  knowledge  of  a  few  important 
facts,  which  are  becoming  wellknown  to-day,  will  do  much 
towards  checking  tuberculosis.  Chief  among  these  facts  arej 
the  following: 

1.  The  disease  is  not  hereditary,  and  parents  do  not  hanc 
it  down  to  their  children. 

2.  It  is  contagious;  that  is,  one  person  may  give  it  to  an- 
other. The  child  may  *'  catch  it  "  from  Lis  parents,  but  he 
does  not  inherit  it. 

3.  The  germs  may  be  carried  in  the  air. 

4.  Dried  sputum,  or  dried  scrofulous  discharges  may  con- 
tain the  germs  of  tuberculosis. 

5.  Every  one  has  considerable  power  of  resisting  the  disease] 
this  ability  is  increased  by  out-door  life  and  good  food;  it  is 
decreased  by  in-door  life,  sedentary  habits,  poor  food  and  h] 
the  use  of  alcoholic  drinks. 

6.  Cows  sometimes  have  tuberculosis,  and  their  milk  may] 
contain  the  germs. 

The  forces  which  can  be  marshalled  against  this  dread  foej 
may  thus  be  easily  deduced.  Each  individual  should  tak( 
plenty  of  out-door  exercise,  he  should  eat  good,  but  not  to( 
rich  food,  and  should  let  alcoholic  drinks  alone.  He  should  be 
careful  to  use  only  such  milk  as  comes  from  unquestionable 
sources,  unless  he  first  sterilizes  or  pasteurizes  it.     When  in 


THE  RESPIRATORY  ORGANS  187 

the  presence  of  a  consumptive,  one  should  avoid  breathing 
air  close  to  him  while  he  is  coughing  and  should  take  especial 
care  not  to  contaminate  one's  hands  or  clothing  with  the 
sputum  of  the  patient.  To  guard  the  public  against  the  dis- 
ease, there  should  be  rigid  insistence  upon  the  carrying  out  of 
certain  rules  to  prevent  the  dissemination  of  infectious 
material  from  the  patient.  The  sputum  should  be  burned. 
Spitting  should  not  be  allowed  in  public  places.  The  rules 
given  by  the  Charity  Organization  of  New  York  are  so  valu- 
able that  they  may  be  repeated  here. 

"Consumption  can  often  be  cured  if  its  nature  be  recognized  early  and 
if  proper  means  be  taken  for  its  treatment.  In  a  majority  of  cases  it  is  not 
a  fatal  disease. 

"Consumptives  are  warned  against  the  many  widely  advertised  cures. ^ 
specifics  and  special  methods  of  treatment  of  consumption.  No  cure  can  be 
expected  from  any  kind  of  medicine  or  method,  except  the  regularly  accepted 
treatment,  which  depends  upon  pure  air,  an  out-of-door  life  and  nourishing 
food. 

"Consumption  is  a  disease  of  the  lungs,  which  is  taken  from  others, 
and  is  not  simply  caused  by  colds,  although  a  cold  may  make  it  easier  to 
take  the  disease.  It  is  caused  by  very  minute  germs,  which  usually  enter 
the  body  with  the  air  breathed.  The  matter  which  consumptives  cough 
or  spit  up  contains  these  germs  in  great  numbers — frequently  millions  are 
discharged  in  a  single  day.  This  matter,  spit  upon  the  floor,  wall  or  else- 
where, dries  and  is  apt  to  become  powdered  and  float  in  the  air  as  dust. 
The  dust  contains  the  germs,  and  thus  they  enter  the  body  with  the  air 
breathed.  This  dust  is  especially  likely  to  be  dangerous  within  doors. 
The  breath  of  a  consumptive  does  not  contain  the  germs  and  will  not  pro- 
duce the  disease.  A  well  person  catches  the  disease  from  a  consumptive 
only  by  in  some  way  taking  in  the  matter  coughed  up  by  the  consumptive. 

"  It  is  not  dangerous  to  live  with  a  consumptive,  if  the  matter  coughed 
up  by  him  be  promptly  destroyed.  This  matter  should  not  be  spit  upon 
the  floor,  carpet,  stove,  wall  or  sidewalk,  but  always,  if  possible,  iri  a  cup 
kept  for  that  purpose.  The  cup  should  contain  water  so  that  the  matter 
will  not  dry,  or  better,  carbolic  acid  in  a  five  per  cent  water  solution  (six 
teaspoonfuls  in  a  pint  of  water).  This  solution  kills  the  germs.  The  cup 
should  be  emptied  into  the  water  closet  at  least  twice  a  day,  and  carefully 
Washed  with  boiling  water. 

"Great  care  should  be  taken  by  consumptives  to  prevent  their  hands. 


198  ADVANCED  PHYSIOLOGY 

face  and  clothing  from  becoming  soiled  with  the  matter  coughed  up.  If 
they  do  become  thus  soiled,  they  should  at  once  be  washed  with  soap  and 
hot  water.  Men  with  consumption  should  wear  no  beards  at  all,  or  only 
closely  cut  mustaches.  When  consumptives  are  away  from  home,  the 
matter  coughed  up  should  be  received  in  a  pocket  flask  made  for  this  pur- 
pose. If  cloths  must  be  used,  they  should  be  immediately  burned  on  re- 
turning home.  If  handkerchiefs  be  used  (worthless  cloths,  which  can  be 
at  once  burned,  are  far  better),  they  should  be  boiled  at  least  half  an  hour 
in  water  by  themselves  before  being  washed.  When  coughing  or  sneezing, 
small  particles  of  spittle  containing  germs  are  expelled,  so  that  consump- 
tives should  always  hold  a  handkerchief  or  cloth  before  the  mouth  during 
these  acts;  otherwise,  the  use  of  cloths  and  handkerchiefs  to  receive  the 
matter  coughed  up  should  be  avoided  as  much  as  possible,  because  it 
readily  dries  on  these,  and  becomes  separated  and  scattered  into  the  air. 
Hence,  when  possible,  the  matter  should  be  received  into  cups  or  flasks.  Paper 
cups  are  better  than  ordinary  cups,  as  the  former  with  their  contents  may 
be  burned  after  being  used.  A  pocket  flask  of  glass,  metal,  or  pasteboard 
is  also  a  most  convenient  receptacle  to  spit  in  when  away  from  home.  Cheap 
and  convenient  forms  of  flasks  and  cups  may  be  purchased  at  many  drug 
stores.  Patients  too  weak  to  use  a  cup  should  use  moist  rags,  which  shouk 
at  once  be  burned.  If  cloths  are  used  they  should  not  be  carried  loose 
the  pocket,  but  in  a  water-proof  receptacle  (tobacco  pouch),  which  shoulc 
be  frequently  boiled.  A  consumptive  should  never  swallow  his  expectorf 
tion. 

"A  consumptive  should  have  his  own  bed,  and  if  possible,  his.oT 
room.     The  room  should  always  have  an  abundance  of  fresh  air — tl 
window  should  be  open  day  and  night.     The  patient's  soiled  wash-clothe 
and  bed  linen  should  be  handled  as  little  as  possible  when  dry,  but  shoi 
be  placed  in  water  until  ready  for  washing. 

"If  the  matter  coughed  up  be  rendered  harmless,  a  consumptive  ma^ 
frequently  not  only  do  his  usual  work  without  giving  the  disease  to  other 
but  may  also  thus  improve  his  own  condition  and  increase  his  chances 
getting  well." 

The  simple  discovery  that  a  little  parasite  is  the  cause  o| 
this  disease,  has  been  the  means  of  saving  many  thousanc 
of  lives.     This  seems  hardly  credible,  for  the  discovery 
the  cause  does  not  tell  us  of  any  cure.     But  it  has  shown 
where  the  danger  lies,  and  we  can  much  better  protect  our-j 
selves  from  a  known  than  from  an  unknown  danger.     At  al 
events,  since  Prof.  Koch  discovered  the  cause  of  tuberculosisj 


THE  RESPIRA'IURY  ORGANS  189 

the  number  of  deaths  has  been  steadily  decreasing.  In  Massa- 
chusetts, for  example,  while  in  1870  the  number  of  deaths  was 
thirty-six  in  ten  thousand,  there  are  about  eighteen  in  ten 
thousand  at  the  present  time.  Tuberculosis  is  largely  a  pre- 
ventable disease,  and  if  each  person  will  do  what  he  can  to 
pass  along  information  as  to  its  cause  and  the  methods  of 
avoiding  it,  he  will  help  to  reduce  the  number  of  cases. 

Pleurisy. — The  ease  of  motion  which  we  have  noticed  in 
the  lungs  is  dependent  upon  the  free  moving  of  the  layers  of 
the  pleura  upon  each  other,  and  this  in  turn  is  dependent  up- 
on the  presence  of  a  watery  liquid  secreted  by  their  glandular 
surfaces.  It  sometimes  happens  that  the  pleura  ceases  to 
perform  its  proper  function,  becomes  inflamed,  or  adheres  to 
adjacent  tissues.  In  all  such  cases  the  movements  of  the 
lungs  become  difficult  and,  as  a  result,  breathing  is  not  so 
free  and  sometimes  becomes  distinctly  painful.  The  trouble 
is  called  pleurisy,  and  may  result  from  various  causes,  of 
which  a  common  cold  is  one.  While  painful,  this  trouble  is 
rarely  dangerous,  and  usually  passes  off  with  proper  treat- 
ment at  the  hands  of  a  physician. 


CHAPTER  XIII 


THE  MECHANISM  AND  CHEMISTRY  OF  RESPIRATION 


txiernat 
'  Infercosfals 


Iniernal 
Infercosfals 


In  the  preceding  chapter  we  have  been  following  the  course 
by  which  air  passes  from  the  exterior  to  the  innermost  cham- 
bers of  the  lungs.    But. 
the  reason  air  enters 
and   leaves  the  lungs 
as  we  breathe  is   not 
explained    by    merely 
noting    the    construc- 
tion of  these  passages; 
for  in  spite  of  the  va- 
rious tissues   compos- 
ing them,  these  tubes 
are    of   themselvei 
powerless     to     inhale 
even  the  smalles: 
quantity  of  air.     W« 
often  say   "the  lungd 
fill  with  air'^;  but  w( 
do  not  appreciate  their^ 
entire     helplessness, 
their  lack  of  ability  to 
make  the  least  move- 
ment    of    their    own 
accord.       The      lungs 
because    air    is    driven 


Fig.  101. — The  attachments  of  the  ribs 
to  the  back  bone  and  sternum 

To  show  their  relations  in  breathing.  Between  one 
pair  of  ribs  is  [shown  the  external  intercostal 
muscles  and  between  a  second  pair  the  internal 
intercostals,  all  other  muscles  being  omitted. 


never  fill  of 
into  them. 


themselves;    they    fill 


THE  MECHANISM  OF  RESPmATION 

Air  is  drawn  into  the  lungs  just  as  it  is  into  a  bellows. 
When  the  space  inside  the  bellows  is  increased  air  must  rush 

190 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION        191 

in  through  the  openings  left  for  that  purpose  or  a  vacuum  is 
formed.  The  thoracic  cavity  is  absolutely  air  tight;  there- 
fore, any  motion  which  will  enlarge  the  cavity  of  the  chest 
will  draw  air  into  the  lungs.  The  chest  is  so  constructed 
that  it  can  be  enlarged  in  two  different  ways,  (1)  by  rib  mo- 
tion and  (2)  by  diaphragm  motion. 

Rib  Breathing. — The  ribs  in  the  body  are  inclined  down- 
ward and  forward;  Fig.  101.  They  are  hinged  to  the  back- 
bone and  if  their  outer  ends  are  lifted,  the  sternum  will  be 
Ufted  and  carried  forward.  This  pushing  forward  of  the 
outer  ends  of  the  ribs  increases  the  distance  from  the  back- 
bone to  the  sternum,  and  thus  enlarges  the  cavity  of  the 
thorax.  The  ribs  are  raised  and  lowered  by  two  sets  of 
muscles,  arranged  between  them,  called  the  intercostals; 
Fig.  101.  When  the  external  intercostals  contract  they  lift  up 
the  ribs,  pushing  forward  the  breastbone;  when  the  internal 
intercostals  contract  they  pull  the  ribs  down,  thus  drawing  the 
breastbone  inward.  But  these  same  motions  of  the  ribs  cause 
the  chest  cavity  to  enlarge  and  decrease  in  size  laterally  also. 
This  increase  from  side  to  side  can  be  understood  if  we  im- 
agine a  pail  with  two  handles,  one  hanging  down  on  either 
side.  If  the  handles  are  raised,  each  leaves  the  side  of  the 
pail,  and  the  distance  between  their  outer  curvatures  is  greater 
than  when  hanging  down.  In  precisely  the  same  way,  when 
the  external  intercostal  muscles  raise  the  ribs  the  distance 
between  their  curved  sides  is  increased,  for  in  their  natural 
position  they  lie  inclined  downward  along  the  sides  of  the 
body.  When  pulled  back  again  to  this  position,  the  distance 
between  their  sides  is  lessened  and  the  thoracic  cavity  is  made 
smaller. 

From  the  method  of  their  attachment  to  the  vertebrae  the 
libs  can  move  only  up  and  down.  Bj^  looking  at  Fig.  123, 
I)age  253,  and  imagining  a  rib  attached  to  the  centrum  and  then 
tied  by  ligaments  to  the  transverse  process  also,  one  sees  that 
the  rib  can  move  in  but  the  one  plane  like  a  metal  hinge  joint. 

It  is  evident  then  that  whenever  the  external  intercostals 


192 


ADVANCED  PHYSIOLOGY 


contract  and  lift  the  ribs,  the  chest  cavity  is  enlarged  and  as 
a  result  air  will  be  drawn  in  to  fill  the  enlarged  space.  This 
forcing  of  the  air  into  the  lungs  is  called  an  inspiration.  When 
later  the  ribs  fall  downward  again  the  chest  cavity  is  con- 
tracted and  the  air  is  forced  out,  producing  an  expiration* 
It  is  a  muscular  effort  to  raise  the  ribs  and  inspire  air,  but  they 
fall  back,  in  part  at  least,  of  their  own  weight. 


Fig.  102, — Diagram 

Illustrating  the  mechanism  of  diaphragm  breathing.  It  represents  the  lungs  of  soi 
small  animal  in  a  closed  bell  glass.  As  the  rubber  membrane  below  is  pulled  do\ 
enlarging  the  cavity,  air  rushes  in  through  the  tube  that  represents  the  trache 
and  the  lungs  enlarge.  (Tigerstedt) 

Diaphragm  Breathing. — When  at  rest  the  diaphragm  is  noj 
stretched  across  the  bottom  of  the  thoracic  cavity  in  a  flaj 
plane,  but   arches   upwards  on  all  sides;    Fig.  46,  page 
Its  shape  thus  causes  it  to  project  into  the  thorax  and  decrease 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION        193 

the  size  of  that  cavity.  The  center  of  the  diaphragm  is  a 
tough  membrane,  from  the  edges  of  which  muscles  radiate 
to  the  walls  of  the  cavity.  When  these  muscles  contract, 
the  center  of  the  diaphragm  is  drawn  downward  and  the 
whole  structure  takes  a  more  nearly  flat  position.  In  doing 
this  the  diaphragm  presses  upon  the  stomach  and  other  ab- 
dominal organs,  forcing  them  downward  and  outward.  Thus 
the  chest  cavity  is  increased  (Fig.  102),  and  air  is  sucked  into 
the  lungs,  which  swell  and  fill  the  enlarged  space. 

At  each  expiration  the  muscles  of  the  diaphragm  relax, 
and  the  muscles  of  the  abdomen  which  were  stretched  some- 
what when  the  organs  in  it  were  pressed  downward,  now 
shorten,  and  the  diaphragm  is  thus  carried  up  into  its  former 
dome-like  shape;  the  room  in  the  thoracic  cavity  is  conse- 
quently lessened,  and  air  is  forced  out  of  the  lungs.  Breathing 
may  thus  be  accompanied  by  a  rise  and  fall  of  the  abdominal 
walls,  but  this  does  not  mean,  of  course,  that  air  is  taken  into 
that  cavity;  merely  that  the  contained  organs  are  displaced 
at  the  descent  of  the  diaphragm,  and  that  the  abdominal 
muscles  force  them  back  again  when  the  diaphragm  relaxes. 

The  reason  that  air  rushes  into  the  lungs  when  the  thoracic 
cavity  is  enlarged  is  that  air  is  constantly  exerting  a  pressure 
upon  our  bodies  equivalent  to  fifteen  pounds  to  the  square 
inch.  As  soon  as  the  thoracic  cavity  is  enlarged,  air  naturally 
enters  it,  since  otherwise  there  would  be  a  vacuum. 

EXTERNAL  AND  INTERNAL  RESPIRATION 

The  alternate  inflow  and  outflow  of  air  through  the  passages 
is  the  most  superficial  part  of  the  breathing  process.  All  the 
air  in  these  passages  is  still  connected  from  the  outside  world, 
and  is  not  yet  a  part  of  the  body  in  any  sense  whatever.  This 
tidal  flow  inward  and  outward  is  called  external  respiration . 

Through  the  thin  walls  of  the  air  sacs  of  the  lungs  the  oxygen 
of  the  air  passes,  following  the  law  of  osmosis  of  gases,  and  com- 
bines with  the  haemoglobin  of  the  red  blood  corpuscles,  as  de- 


194  ADVANCED  PHYSIOLOGY 

scribed  on  page  124.  From  the  lung  region  the  blood  hurries  to 
the  innumerable  cells  of  the  body  each  of  which  is  needing 
its  share  of  food  and  oxygen.  From  the  capillaries  these  pass 
into  the  lymph  which  surrounds  the  cells,  and  thence  through 
the  cell  walls  into  the  protoplasm.  This  final  step  is  the  most 
important  of  the  entire  respiratory  process,  and  is  naturally 
called  internal,  or  tissue  respiration. 

Up  to  this  point  the  respiratory  process  has  been  described 
as  though  serving  only  to  carry  oxygen  to  the  cells;  but  this  is 
only  half  the  story,  for  in  the  cell  protoplasm  numerous  ele- 
ments combine  with  oxygen,  and  among  other  things  c^i'l^on 
dioxid  is  thus  formed.  This  passes  out  of  the  cells,  into  tn« 
lymph,  thence  into  the  plasma  of  the  blood  (not  into  the  hae- 
moglobin save  in  very  limited  degree)  and  is  carried  to  the  lungs ; 
here  it  dialyzes  through  into  the  air  sacs,  and  then  is  expelled 
during  expiration. 

NERVOUS  CONTROL  OF  RESPIRATORY  MOVEMENTS 

That  breathing  is  under  the  guidance  of  the  nervous  system! 
is  evident.     One  can  breathe  fast  or  slowly  at  will;  one  breathes) 
faster  when  he  is  running  than  when  he  is  still,  and  faster] 
when  he  is  excited  than  when  he  is  calm.     These  changes  in 
the  rate  of  breathing  generally  take  place  without  any  thought 
whatever;  but  they  are,  nevertheless,  brought  about  under 
the  direction  of  the  brain.     Unlike  the  heart,  the  breathing 
muscles  are  not  automatic,  and  unless  stimuli  come  to  them 
from  the  central  nervous  system  they  will  not  act.     The 
source  of  these  stimuli  is  in  the  lower  part  of  the  brain, 
in    the    medulla,   at  the    place    known    as    the    respiratory 
center. 

No  nerves  go  directly  from  the  respiratory  center  to  the 
intercostal  muscles  or  diaphragm;  they  first  go  down  in  the 
spinal  cord  for  some  distance  and  then  pass  out  in  nerves 
which  leave  between  the  vertebrae.  One  set  of  nerve  fibres 
an  each  side  of  the  body  leaves  the  spinal  cord  in  the  neek 


iMECIIANISM  AND  CHEMISTRY  OF  RESPIRATION        195 


Head 


\\f\Respiratoiy 
Centre 


\Nerve  to 
wiaphrqgm 

W^^nfercostal 

to  Rib 
'Muscfci 


region  (Fig  103);  each  set  passes  out  of  the  cord  by  three 
roots,  i.e.  by  nerves  between  the  second  and  third,  third  and 
fourth,  fourth  and  fifth  vertebrae.  These  roots  unite  to 
form  a  single  nerve  on  each  side  which  passes  down  through 
the  thorax  behind  the  lungs  and  then  spreads  out  in  the 
muscles  of  the  diaphragm.  Messages  go  over  these  phrenic 
nerves  from  the  respiratory  center 
to  the  diaphragm,  but  none  go  in 
the  opposite  direction;  Fig.  103. 
The  second  set  of  fibres  from  the 
respiratory  center,  the  intercostal 
nerves,  go  farther  down  the  cord  to 
the  region  of  the  ribs  to  emerge 
between  the  vertebrae  and  pass  at 
once  into  the  intercostal  muscles; 
Fig.  103. 

If  these  nerves  which  carry  these 
impulses  from  the  respiratory  center 
to  the  various  muscles  concerned  in 
breathing  are  cut,  or  if  that  center 
itself  is  destroyed,  breathing  stops 
at  once  and  death  follows.  As  long 
as  the  respiratory  center  is  active,  it 
sends  out  stimuli  to  the  breathing 
muscles  with  perfect  regularity.  The 
action  of  this  center  is  partly  in- 
voluntary, i.  e.  goes  on  without  any 
action  of  the  will,  as  is  shown  by  the 
fact  that  breathing  continues  while 
one  is  asleep.  At  the  same  time,  that 
the  center  is  partly  voluntary  is 
demonstrated  by  the  fact  that  one 

can  at  any  time  breathe  fast  or  slowly  as  he  wishes. 
During  normal  life  the  average  rate  at  which  respiratory 
impulses   are    sent   to   the  muscles  concerned  is  fifteen  to 


Fig.  103. — Showing  thb 
origin  of  the  nerves 
controlling  breathing 


196  ADVANCED  PHYSIOLOGY 

twenty  per  minute.     In  case  of  sickness,  especially  in  fevers, 
this  rate  may  be  much  more  rapid. 

Thus,  although  the  stimuh  for  breathing  all  come  from  the 
same  general  center,  they  go  to  the  muscles  by  different 
courses.  Since  all  breathing  impulses  start  from  the  brain 
it  is  evident  that  if  the  neck  be  broken  so  as  to  cut  off  all  con- 
nection of  these  muscles  with  the  brain,  breathing  will  stop 
at  once.  If,  however,  the  neck  should  be  broken  below  the 
place  where  the  phrenic  nerves  leave  the  cord,  the  diaphragm 
would  still  be  connected  with  the  respiratory  center  and  might 
still  be  capable  of  making  respiratory  movements.  Under 
such  circumstances  persons  have  lived  for  years,  although  the 
lower  part  of  the  body  was  cut  off  from  the  brain  and  of  course 
paralyzed. 

The  intercostal  and  phrenic  nerves  carry  messages  away 
from  the  brain;  probably  never  toward  it. 

One  pair  of  nerves,  however,  carries  messages  from  the 
lungs  to  the  brain;  these  are  the  respiratory  branches  of  the 
vagus  nerves;  Fig.  77,  p.  144.  The  messages  which  go  over 
these  respiratory  branches  are  not  for  arousing  movements, 
but  for  informing  the  respiratory  center  of  conditions  in  the 
lungs,  thus  affecting  the  messages  going  to  the  muscles  of  the 
diaphragm  and  ribs  which  are  then  modified  to  meet  the 
circumstances.  I 

The  rate  and  nature  of  breathing  are  not  only  affected  by 
direct  messages  from  the  lungs,  but  by  stimuli  from  the  nose 
lining.  Fumes  from  ammonia  or  sulfur  will  practically  stop 
breathing  processes  for  a  short  time.  Moreover,  sudden  pain 
in  the  abdomen  may  be  followed  by  a  cessation  of  breathing. 
Dashes  of  cold  water  will  set  up  more  rapid  breathing  at  first, 
though  later  it  may  be  followed  by  a  slower  respiration.  None 
of  these  influences  on  the  body  surface  affects  the  breathing 
muscles  directly;  sensations  go  from  the  surface  to  the 
brain  and  then  act  indirectly  through  the  respiratory 
center. 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       197 


THE  CAPACITY  OF  THE  LUNGS 


Complemental  Air 

100  Cv  in . 

Air  that  can  be  taken 
in  with  a  deep  breath 


Tidal  Air      3ocu  in. 
Taken  in  with  each  breath. 


With  each  inspiration,  a  certain  amount  of  air  is  drawn 
into  the  lungs  and  with  each  expiration  it  is  forced  out.  The 
lungs,  however,  are  never  completely  emptied  in  expiration 
and  never  filled  in  an  ordinary  inspiration.  At  each  inspira- 
tion, the  average  person  takes  into  his  lungs  about  30 
cubic  inches  of  new  air.  This  is  called  the  tidal  air.  With 
some  effort,  about  100  cubic  inches 
of  complemental  air  can  be  inhaled  and 
exhaled  in  addition  to  the  tidal  air. 
After  an  expiration  of  the  tidal  air,  one 
can,  by  effort,  expel  an  additional  100 
cubic  inches  of  so-called  supplemental 
air.  Even  after  the  greatest  effort 
of  expiration  there  remain  in  the  lungs 
about  60  cubic  inches  of  residual  air 
which  cannot  be  expelled;  Fig.  104. 
These  figures  are  only  the  average,  and 
different  individuals  have  very  differ- 
ent breathing  habits,  i.e.  some,  even  in 
quiet  breathing,  inspire  three  times  as 
much  air  as  others. 

Thus  with  an  ordinary  breath  only 
about  30  cubic  inches  of  the  190 
cubic  inches  of  air  in  the  lungs  of  the 
normal  individual  is  changed.  The 
larger  bronchi  can  hold  10  cubic 
inches  of  air  without  much  difficulty 
and,  therefore,  much  of  the  air 
breathed  in  and  out  is  merely  used  in  ventilating  these  tubes. 
Hence  the  air  in  the  deepest  parts  of  the  lungs — that  in 
the  alveoli,  or  air  sacs — is  not  wholly  changed.  The  lungs, 
therefore,  are  never  entirely  filled  with  fresh  air.  The  only 
way  that  fresh  air  usually  gets  into  the  air  sacs,  where    it 


Supplemental  Air 

100  Cu.  in 

Air  that  can  be  expelled 
with  a  deep  expiration 


/Residual  Air 

60  Cu.  in. 

Air  that  cannot  be 
driven  from  the  lun^s 


Fig.  104. — Diagram 

Showing  relative  amoun*. 
of  air  in  lungs  under  dii- 
ferent  circumstances. 


198  ADVANCED  PHYSIOLOGY 

comes  in  contact  with  the  blood,  is  by  gradual  passage, 
or  by  diffusion,  from  the  larger  air  tubes  into  the  smaller 
sacs. 

BREATHING  HABITS 

Certain  practical  lessons  as  to  methods  of  breathing  may 
be  drawn  from  these  facts.  Diaphragm  breathing  fills  the 
lungs  at  their  lowest  point,  rib  breathing  tends  to  fill  the 
upper  lobes.  Either  of  these  types  alone  will  produce  only 
a  partial  action  of  the  lungs,  and  if  one  accustoms  himself  to 
only  one  type  of  breathing,  parts  of  his  lungs  are  liable  to 
become  sluggish.  This  inactive  condition  produces  a  tendency 
to  lung  diseases,  e.g.  consumption,  which  generally  starts  in 
the  least  used  lobes  of  the  lungs.  Breathing  should,  therefore, 
involve  the  whole  lung  equally;  neither  rib  nor  diaphragm 
breathing  should  predominate.  Among  people  who  are  not 
hampered  by  ill  devised  clothing,  both  ribs  and  diaphragm 
act  freely  in  natural  breathing.  Our  methods  of  dress  inter- 
fere with  this  freedom.  Corsets,  tight  bands  around  the 
waist,  and  the  custom  of  supporting  the  skirts  from  the  hips, 
interfere  with  women's  abdominal  breathing.  Men  have  a 
tendency  to  make  the  breathing  too  exclusively  abdominal. 
They  should  give  particular  attention  to  developing  rib,  or 
chest  breathing,  while  women  should  especially  try  to  strength- 
en their  abdominal  breathing.  This  can  easily  be  done  if  a 
little  attention  be  given  to  the  matter  each  day.  Unneces- 
sary or  needlessly  tight  bands  about  the  waist  are  used  only 
by  those  who  see  beauty  in  a  weakened,  misshapen  form, 
and  who  hold  health  a  cheap  possession. 

In  an  active,  out-of-door  life,  like  that  led  by  children, 
soldiers  or  mountaineers,  vigorous  exercise  causes  very  rapid 
breathing  and  thus  keeps  the  lungs  active.  But  the  quiet 
life  of  adults  in  cities  does  not  involve  much  exercise,  and 
the  lungs  are  rarely  filled  with  fresh  air.  For  this  reason  it  is 
a  very  good  practice  for  city-dwellers  to  take  several  long 


MECHAJNISM  AND  CHEMISTRY  OF  RESPIRATION        199 

breaths  several  times  a  day,  filling  and  emptying  the  lungs  as 
completely  as  possible. 

CAUSE  OF  RESPIRATORY  MOVEMENTS 

The  Cause  of  Respiratory  Movements. — None  of  these  facts, 
however,  tell  us  much  about  the  real  purpose  of  respiration 
or  the  actual  cause  of  the  respiratory  movements;  they 
only  describe  how  the  movements  are  produced  and 
regulated. 

The  respiratory  movements  are  started  in  the  respiratory 
center  which  sends  regular,  rhythmical  messages  down  the 
cord  to  the  breathing  muscles.  What  excites  this  center  into 
such  regular  activity?  In  answer  to  this  question  an  interest- 
ing experiment  may  be  described.  By  a  complicated  method 
it  is  possible  to  send  through  the  brain,  and  thus  through  the 
respiratory  center,  blood  different  from  that  which  goes  to  the 
rest  of  the  body.  If  blood  containing  only  a  small  amount 
of  oxygen  is  sent  through  it,  the  center  begins  to  send  out 
messages  very  rapidly  to  the  breathing  muscles,  even  though 
the  rest  of  the  body  is  receiving  very  pure  blood.  On  the 
other  hand,  if  the  blood  sent  through  the  respiratory  center 
contains  an  unusually  large  proportion  of  oxygen,  the  breath- 
ing messages  are  sent  out  more  slowly  than  usual.  If  blood 
with  an  extremely  large  amount  of  oxygen  be  used,  breathing 
messages  become  very  slow  no  matter  what  kind  of  blood  the 
rest  of  the  body  receives. 

The  logical  conclusion  is  that  the  center  in  the  brain,  which 
controls  breathing,  is  influenced  by  the  condition  of  the 
blood  which  flows  through  it.  When  the  body  is  doing  more 
work  than  usual,  more  oxygen  is  needed,  and  more  carbon 
dioxid  is  being  formed.  The  blood  rapidly  loses  the  oxygen 
and  absorbs  carbon  dioxid;  this  impure  blood  affects  the  nerve 
cells  of  the  medulla,  causing  more  rapid  breathing.  It  is  the 
condition  of  the  blood  in  the  respiratory  center  that  ordinarily 
determines  the  rate  of  respiratory  movements. 


200  ADVANCED  PHYSIOLOGY 


THE  CHEMISTRY  OF  RESPIRATION 

Respiration  is  a  process  of  the  absorption  and  elimination 
of  gases  which  occurs  in  all  animals.  Not  all  animals,  how- 
ever, have  lungs.  Fishes  have  gills  for  this  purpose;  some  ani- 
mals (earthworms)  can  take  sufficient  amounts  of  these 
gases  through  the  skin  and  need  no  lungs,  gills  or  any  special 
respiratory  organs.  Yet  these  same  animals,  if  not  allowed 
to  get  rid  of  carbon  dioxid  and  take  in  oxygen,  shortly 
die.  To  understand  respiration  we  must,  therefore,  study 
the  relation  of  these  gases  to  the  blood. 

Changes  in  the  Air  During  Breathing. — 1.  Inhaled  air  con- 
tains about  twenty  per  cent  of  oxygen,  while  exhaled  air  con- 
tains only  sixteen  per  cent,  showing  that  oxygen  is  extracted 
from  the  air  while  passing  through  the  lungs. 

2.  Inhaled  air  contains  no  carbon  dioxid,  or  only  slight 
traces  of  it,  while  exhaled  air  contains  four  per  cent.  Carbon 
dioxid  is,  therefore,  added  to  the  air  during  respiration. 

3.  Inhaled  air  has  a  temperature  which  varies  with  the 
conditions.  On  a  cold  winter  day,  it  may  be  below  zero;  on 
a  hot  summer  day,  it  may  be  as  high  as  one  hundred  degrees; 
ordinarily  it  will  be  in  the  vicinity  of  seventy  degrees,  the 
temperature  at  which  our  rooms  are  usually  kept.  Exhaled 
air  is  found  to  be  very  nearly  ninety-eight  degrees,  the  body 
temperature.  Although  there  is  some  variation  in  the  tem- 
perature of  exhaled  air,  it  is  never  much  below  this  point. 
If  the  air  is  inhaled  at  70°  F.,  it  will  evidently  be  warmed 
in  its  passage  through  the  lungs,  and  the  body  become 
cooled  in  consequence. 

4.  The  amount  of  moisture  in  the  inhaled  air  is  variable. 
On  a  dry  day  it  is  very  slight,  while  on  a  wet  day  it  is  very 
great;  but  exhaled  air  always  contains  nearly  as  much  moist- 
ure as  it  can  hold.  This  can  easily  be  seen  by  breathing  upon 
a  piece  of  cold  glass.  The  exhaled  air,  when  cooled  by  the 
glass,  cannot  hold  as  much  moisture  as  when  it  was  warm. 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       201 

and  moisture  is  deposited  on  the  glass  in  the  form  of  small 
drops  of  water.  This  saturation  of  exhaled  air  shows  that 
it  has  extracted  water  from  the  body. 

The  lining  of  the  lungs  is  the  tissue  through  which  these 
exchanges  are  made;  it  is  a  membrane,  moist  because  covered 
with  unicellular  mucous  glands,  and  thus  always  flexible  and 
not  dried  by  the  ever-changing  air.  Because  of  the  nature  of 
its  structure,  gases  diffuse  through  it  even  more  readily  than 
they  would  go  through  a  pure  water  film  of  the  same  thickness. 
In  the  instance  of  carbon  dioxid,  diffusion  is  three  times  as  fast 
through  lung  tissue,  as  through  a  water  membrane  of  equal 
thickness.  The  actual  thickness  of  the  wall  of  a  lung  alveolus 
is  about  1-6250  of  an  inch  (0.004  mm.) 

Changes  in  the  Blood. — The  changes  in  the  blood  are,  of 
course,  just  the  reverse  of  those  in  the  air.  What  the  air 
absorbs,  the  blood  has  given  up,  and  what  the  air  has  lost,  the 
blood  has  absorbed.  From  these  simple  facts  we  learn  that 
the  blood  takes  oxygen  from  the  air,  but  gives  up  to  the  air 
carbon   dioxid,    heat   and   moisture. 

How  Oxygen  Gets  into  the  Blood. — When  the  blood  flows 
through  the  small  capillaries  in  the  walls  of  the  alveoli  of  the 
lungs  (Fig.  99),  it  comes  very  close  to  the  air,  so  close  that 
gases  readily  pass  from  the  air  to  the  blood.  The  air  contains 
oxygen  in  large  amounts  and  under  considerable  pressure; 
as  a  result  some  of  it  is  at  once  absorbed  by  the  liquid  plasma 
of  the  blood.  There  is  nothing  unusual  in  this  fact,  for  water 
or  any  other  liquid  will  absorb  gases  from  the  air.  Oxygen 
is  forced  into  water  by  the  pressure  of  air  (15  lbs.  to  the 
sq.  in.)  on  its  surface.  If  water  is  placed  in  a  closed  chamber 
from  which  all  the  air  is  then  removed,  this  is  very  evident, 
for  the  air  dissolved  in  the  liquid  will  come  away  from  it  in 
bubbles.  Contrariwise,  if  the  pressure  of  air  or  other  gases 
above  the  water  surface  is  increased,  the  gases  are  absorbed  in 
just  the  degree  that  the  pressure  is  increased.  So  too,  carbonic 
9icid  gas  is  forced  into  water^  to  form  soda  or  Seltzer  water^  and 


202  ADVANCED  PHYSIOLOGY 

the  bubbles  of  gas  can  be  seen  coming  out  of  such  water  when 
the  pressure  is  released. 

The  amount  of  oxygen  which  the  blood  absorbs  in  this  way 
is  very  small;  by  far  the  larger  part  is  not  simply  absorbed 
but  chemically  combined  with  the  red  coloring  matter,  or 
haemoglobin. 

Haemoglobin. — We  have  already  seen  that  the  blood  con- 
tains red  corpuscles,  which  are  like  little  sponges  holding  in 
solution  a  material  called  haemoglobin;  page  124.  This  sub- 
stance has  an  affinity  for  oxygen,  and  provided  the  gas  is 
under  slight  pressure,  will  absorb  it  in  large  amounts  when- 
ever in  contact  with  it.  After  haemoglobin  has  absorbed 
oxygen,  it  is  a  bright  crimson;  but  if  then  put  in  a  place 
where  there  is  nO  oxygen,  or  where  the  oxygen  pressure  is 
very  slight,  it  will  release  the  oxygen  it  has  absorbed  and  its 
color  will  change  to  a  bluish  red.  Hence  arterial  blood,  which 
has  just  taken  on  oxygen  in  the  lungs,  is  bright  crimson,  while 
venous  blood,  which  contains  less  oxygen,  is  bluish  red  ii 
color. 

Oxygen  can  be  absorbed  by  haemoglobin  because  of  the  iroi 
element  in  it;  by  analysis  it  is  found  that  a  little  over  0.3%  ig 
iron ;  one  molecule  of  oxygen  will  combine  chemically  with  ever] 
atom  of  iron.  The  oxygen  capacity  of  the  blood  is  thus  Km- 
ited ;  but  as  each  corpuscle  hurries  through  the  lung  capillariesj 
it  seizes  what  it  can  absorb  and  hastens  away  to  some  part  of 
the  body  where  the  oxygen  is  needed.  There  is  about  nine- 
teen per  cent  of  oxygen  in  arterial  blood,  most  of  it  being  ii 
the  red  corpuscles. 

How  the  Blood  Gives  up  its  Oxygen. — Let  us  follow  the  bloodj 
and  see  what  becomes  of  its  oxygen.     After  going  back  to  th( 
heart,  from  the  lungs,  and  flowing  out  through  the  arteries,  ii 
finally  comes  to  the  capillaries  in  the  muscles,  glands,  etc.J 
somewhere  in  the  body;  for  example,  in  the  fingers;  Fig.  91. 
Although  it  spends  only  about  one  second  in  the  capillaries  itj 
loses  in  that  short  time  35%  of  its  oxygen.     This  is  because] 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       203 

no  free  oxygen  is  present  in  the  tissues,  since,  as  we  shall  see 
later,  the  muscles  are  using  up  oxygen  as  fast  as  they  can  get 
it.  Here  then,  among  the  tissues  where  the  oxygen  is  nearly 
absent,  or  under  very  slight  pressure,  the  corpuscles  give  up 
the  oxygen  they  are  carrying  and  turn  to  a  bluish  red  color 
as  they  flow  out  from  the  capillaries  into  the  veins  and  back 
to  the  heart. 

Nitrogen  in  Respiration. — Nitrogen  composes  about  four- 
fifths  of  the  air  we  breathe,  but  so  far  as  the  respiratory  pro- 
cesses are  concerned,  it  simply  dilutes  the  oxygen  of  the  air. 
Some  of  it  is  doubtless  absorbed  by  the  blood  plasma  but  none 
of  it  is  used  in  the  body  and  practically  none  of  it  is  given  off 
from  the  body  in  the  form  of  gas.  Hence  the  blood  comes 
back  to  the  lungs  from  the  tissues  with  just  as  much  nitrogen 
as  it  had  originally. 

Breathing  Pure  Oxygen. — The  statement  that  nitrogen 
dilutes  the  air  is,  however,  open  to  a  misapprehension.  If 
oxygen  is  as  active  a  gas  as  we  believe  it  to  be,  what  will  be 
the  effect  if,  instead  of  breathing  an  atmosphere  which  con- 
tains only  one-fifth  oxygen,  we  breathe  pure  oxygen?  We 
might  at  first  imagine  that  we  should  absorb  much  more 
oxygen.  Conversely,  we  might  suppose  that,  if  there  were  less 
than  the  usual  amount  of  oxygen  in  the  air,  we  could  not 
obtain  enough.  We  often  think  that  the  reason  air  in  a 
room  becomes  unpleasant  and  depressing  is  that  it  contains 
so  little  oxygen.  All  of  these  impressions  are  mistakes.  Since 
the  haemoglobin  can  absorb  a  certain  quantity  of  oxygen 
and  no  more,  it  can  obtain  this  amount  perfectly  well  from 
ordinary  air,  or  indeed  from  air  containing  less  oxygen  than 
usual.  If,  therefore,  one  should  breathe  pure  oxygen,  the 
blood  would  take  on  practically  no  more  than  it  does  from 
ordinary  air  (a  sHghtly  greater  amount  might  be  taken  in  by 
the  blood  plasma,  for  that  combination  is  a  mere  mixture). 
So  far  as  the  oxygen  goes,  there  is  probably  enough  in  any  air 
we  breathe  to  furnish  the  blood  properly  for  effective  working. 


204  ADVANCED  PH^SIOLOGV 

Breathing  Carbon  Monoxid. — Carbon  monoxid  (CO)  occurs 
in  all  coal  gas  and  all  illuminating  gas,  sometimes  escaping 
from  stoves  which  are  badly  constructed  or  have  faulty 
drafts.  It  is  carbon  monoxid  which  burns  with  the  blue 
flame  often  seen  flickering  over  the  surface  of  coal  in  a  stove 
or  over  burning  charcoal.  Haemoglobin  will  combine  more 
readily  with  carbon  monoxid  than  with  oxygen,  so  that  if  the 
two  are  in  the  same  air,  carbon  monoxid  will  unite  with  the 
haemoglobin  of  the  blood  and  oxygen  will  be  excluded.  If 
this  happens,  the  person  concerned  will  die  of  suffocation 
just  as  truly  as  if  he  had  stopped  breathing. 

It  is  easy  to  see  why  leaking  gas  pipes  and  stoves  are  un- 
healthful.  Gas  pipes  which  enter  sleeping  rooms  should  be 
watched  with  especial  care,  for  from  a  very  sUght  leak  enough 
escaping  gas  may  accumulate  during  a  night  to  suffocate  a, 
sleeping  person.  There  is  danger,  too,  in  leaving  illuminal 
ing  gas  turned  low,  for  the  flame  may  go  out,  blown  by  a^ 
gust  of  wind,  or  because  the  pressure  is  temporarily  lowered 
at  the  central  plant,  and  the  room  be  filled  with  gas. 

Carbon  Dioxid  in  Respiration. — In  oxidation  some  of  thej 
food  products  unite  with  oxygen  and  as  a  result  another  gasJ 
carbon  dioxid,  is  formed.  When,  for  example,  a  candle  is] 
lighted,  the  tallow  in  it  combines  with  oxygen,  thus  pro- 
ducing carbon  dioxid.  If  the  tallow  were  eaten  it  would,  inj 
a  similar  way,  be  united  with  oxygen  in  the  body  and  thej 
same  gas  would  result.  Since  this  carbon  dioxid  is  a  waste 
product,  it  must  be  removed  from  the  body  in  some  way  and 
the  second  phase  of  the  respiratory  process  is  concerned  withj 
this  elimination. 

Whenever  any  of  the  tissues  of  the  body  are  active,  some 
food  or  tissue  is  combined  with  oxygen  and  a  certain  amount] 
of  carbon  dioxid  is  formed.  The  blood,  as  it  flows  through] 
the  capillaries  of  these  tissues,  absorbs  this  gas  very  much  as 
it  does  oxygen  in  the  lungs,  and  for  the  same  reasons;  i.e. 
because  the  carbon  dioxid  pressure  is  high.     By  the  time! 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       205 

the  blood  has  gone  through  the  capillaries  it  has  become  loaded 
with  this  gas.  About  40%  of  what  the  blood  carries  is  in  loose 
combination  with  the  proteid  materials  in  the  corpuscles,  but 
this  does  not  at  all  effect  the  freedom  with  which  oxygen 
combines  with  the  iron  of  the  haemoglobin.  About  60%  of 
the  carbon  dioxid  is  carried  in  the  plasma;  a  small  part  of  this 
(about  2%)  is  simply  dissolved  in  the  plasma,  while  the  rest  of 
it  is  temporarily  combined  with  other  elements  in  the  blood 
stream. 

When  the  blood  comes  to  the  air  sacs  in  the  lungs  it  finds  con- 
ditions opposite  to  those  among  the  tissues;  the  amount  of 
carbon  dioxid  in  the  inhaled  air  is  very  small,  and  the  pressure 
is  so  low  that  the  blood  immediately  lets  go  its  hold  on  its 
CO2,  which  thus  passes  at  once  into  the  air  sacs.  Thus  carbon 
dioxid  gas  is  breathed  out  at  every  expiration,  while  new  air  is 
breathed  in.  If  this  inhaled  air  should  contain  too  much  CO2, 
the  blood  could  not  rid  itself  of  its  own  quota  of  the  gas,  and 
the  person  would  soon  die. 

It  has  been  found  that  air  containing  8-9%  of  carbon 
dioxid  produces  severe  discomfort. 

This  gas,  which  is  heavier  than  ordinary  air,  is  sometimes 
found  in  abundance  in  deep  wells  or  mines  where  it  accumu- 
lates, making  the  air  distinctly  poisonous.  Men  who  must 
descend  into  such  wells  frequently  first  lower  a  lighted  candle. 
If  it  will  burn,  the  air  is  safe  to  breathe;  if  not,  no  person  can 
safely  enter. 

BREATHING  AND  EXERCISE 

Since  without  a  supply  of  oxygen  one  cannot  live,  and  since 
one  would  soon  be  poisoned  by  carbon  dioxid  if  he  could  not 
dispose  of  it,  the  necessity  of  breathing  is  evident.  We  can 
easily  see,  too,  why  breathing  will  increase  in  rapidity  if  one 
exercises  the  muscles  vigorously,  as,  for  instance,  in  running. 
Breathing  must  be  accelerated  ^0  ^s  \g  keep  up  a  larger  supply 


206  ADVANCED  PHYSIOLOGY 

of  air  in  the  lungs,  because  (1)  the  blood  needs  more  oxygen 
for  carrying  on  its  extra  activity  during  the  running,  and  (2) 
it  is  necessary  to  dispose  of  the  extra  carbon  dioxid  given  off 
by  the  muscles  when  they  are  contracting  rapidly.  But  in- 
creased breathing  alone  will  not  accomplish  this  end.  A 
more  rapid  circulation  of  the  blood  is  needed  to  bring  the 
carbon  dioxid  to  the  lungs,  so  the  heart  begins  to  beat  more 
quickly  and  the  blood  to  flow  more  swiftly.  As  soon  as  the 
blood  circulates  more  rapidly,  however,  and  the  gases  are 
carried  off  sufficiently,  the  necessity  for  quick  breathing  is  in 
part  reduced.  Every  runner  knows  that  after  running  a  few 
minutes,  he  gets  what  is  called  his  ''  second  wind".  Breathing 
grows  less  rapid  and  he  may  keep  on  running  for  a  consider- 
able time  without  any  trouble  with  respiration.  This  "second 
wind"  appears  when  the  circulation  of  the  blood  has  become 
rapid  enough  to  carry  off  properly  the  gases  formed. 

Evils  of  Indoor  Life. — Nature,  apparently,  intended  that 
man  should  live  out  of  doors.  But  we  have  adopted  new 
habits  of  life,  and  shut  ourselves  up  for  many  hours  of  the 
day  in  close  rooms.  Hence,  we  are  forced  to  breathe  air 
which  has,  perhaps,  been  breathed  by  other  people  and  thus 
rendered  unwholesome. 

In  spite  of  its  advantages  living  indoors  is  unnatural,  and  is 
conducive  to  certain  diseases.  People  who  live  out  of  doors 
are  rarely  attacked  by  lung  diseases;  while  they  do  not  entirely 
escape  them,  they  are  affected  much  less  often  than  house- 
dwellers.  Other  diseases  are  rendered  especially  serious 
because  we  live  in  more  or  less  limited  spaces.  But  since  we 
cannot,  in  the  present  state  of  civilization,  pass  all  our  time 
out  of  doors,  we  should  do  our  utmost  to  remedy  these  con- 
ditions by  furnishing  our  rooms  with  a  proper  supply  of  good 
fresh  air. 

Ventilation. — More  attention  is  paid  to  the  proper  ventila- 
tion of  buildings  to-day  than  ever  before.  In  the  times  when 
rougher  materials  were  used  in  their  construction  and  when 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       207 

open  fireplaces  were  the  rule,  so  many  chances  were  left  for 
air  to  enter  houses  that  special  ventilating  apparatus  was 
almost  unnecessary.  With  more  skilled  workmanship,  with 
machine-made  building  materials  and  especially  with  improved 
methods  of  heating,  a  necessity  has  arisen  for  fresh  air  radia- 
tors, fans,  transoms  and  the  various  ventilating  devices. 

The  need  for  ventilating  a  room  depends  on  the  rate  at 
which  the  air  is  breathed  by  its  occupants.  The  normal  per- 
son breathes  from  fifteen  to  twenty  times  a  minute.  When 
quiet  the  muscles  oxidize  materials  slowly  and  the  breathing 
rate  is  lowered,  but  any  hurry  or  excitement  causes  an  im- 
mediate increase  in  the  breathing  rate.  Since  we  know  that 
with  each  breath  about  thirty  cubic  inches  of  air  is  taken  into 
the  lungs,  it  would  be  easy  to  calculate  the  amount  of  air 
breathed  in  any  given  time,  but  this  would  not  really  tell  us 
how  much  air  is  needed.  To  know  this  it  would  be  necessary 
to  find  out  to  what  degree  air  can  be  impure  before  it  is  not 
properly  respirable.  Fresh  air  keeps  one  active  and  alert  but 
the  air  of  a  close  room  makes  one  feel  stupid  and  sleepy,  and 
even  produces  headache.  This  is  not,  as  sometimes  supposed, 
because  there  is  not  enough  oxygen  in  the  air,  for  all  rooms 
contain  sufficisnt  oxygen  to  furnish  the  haemoglobin  with  all 
it  can  hold;  nor  is  the  reason  to  be  found  in  the  presence  of 
an  unusually  large  amount  of  carbon  dioxid.  There  may  be 
about  three  per  cent  of  pure  carbon  dioxid  in  the  air  with- 
out interfering  in  any  degree  with  its  wholesomeness.  So  long 
as  there  is  not  enough  to  interfere  with  the  elimination  of  this 
gas  from  the  lungs,  it  will  do  no  injury,  and  the  air  of  no  or- 
dinary room,  however  poorly  ventilated,  contains  enough  to 
do  this.  The  ill  effects  of  breathing  air  already  breathed  by 
other  persons  are  partly  due  to  the  large  amount  of  water  it 
contains  and  partly  to  its  high  temperature.  Perhaps  other 
factors  are  concerned,  but  the  trouble  is  generally  neither  lack 
of  oxygen  nor  the  presence  of  too  much  carbon  dioxid. 

It  is  therefore  evident  that  it  is  no  simple  matter  to  tell  just 


JOe  ADVANCED  PHYSIOLOGY 


how  much  air  a  person  needs.  Taking  everything  into  con- 
sideration, those  who  have  made  a  special  study  of  ventila-' 
tion  tell  us  that  each  person  should  be  allowed  from  2000 
to  3000  cubic  feet  of  fresh  air  per  hour.  This  amount  would 
be  contained  in  a  room  ten  feet  high,  twenty  feet  long,  and 
ten  feet  wide.  Fortunately,  doors  and  windows  are  always 
loose  enough  to  allow  a  free  passage  of  air  through  the  cracks 
around  them,  for  if  churches,  schoolrooms,  theatres,  etc.,  were 
built  with  air-tight  joints  around  windows  and  doors,  they 
would  have  to  be  made  enormously  large  to  meet  the  demands 
of  the  crowds  which  gather  in  them. 

In  arranging  for  the  ventilation  of  rooms,  it  is  well  to  learn 
and  remember  a  few  general  principles: 

1.  A  room  may  be  well  ventilated,  but  feel  uncomfortable 
because  it  is  too  hot.  The  temperature  should  never  be 
above  70° F,  unless  the  room  is  occupied  by  very  aged  people. 
Public  halls  and  sleeping  cars,  for  example,  are  often  kept  so 
hot  that  they  are  very  uncomfortable,  even  though  there  may 
be  good  ventilation.  On  the  other  hand,  the  temperature 
may  be  right,  but  the  air  may  be  poor.  Too  high  a  tempera- 
ture with  good  ventilation  is,  however,  the  more  common  fault. 

2.  For  proper  ventilation,  a  constant  motion  of  air  is  needed, 
not  simply  around  the  room,  but  from  the  room  to  the  out- 
side. If  proper  means  for  the  escape  of  air  is  provided, 
plenty  of  air  will  come  in  around  doors  and  cracks,  to  take 
the  place  of  that  going  out.  An  open  fire  place  is  one  of  the 
best  methods  of  ventilation.  A  fire  in  a  stove  will  serve  the 
same  purpose,  for  it  is  constantly  sending  heated  gases  up  the 
chimney,  thus  drawing  fresh  air  into  the  room.  The  belief 
that  stoves  are  unhealthful,  because  they  use  up  the  oxygen 
of  a  room,  is  a  great  mistake.  They  use  oxygen,  but  they  are 
constantly  drawing  in  fresh  air  to  replace  it.  On  the  other 
hand,  gas  stoves  or  gas  burners  in  a  room  will  use  up  oxygen; 
for  generally  they  are  not  connected  with  any  chimney  or 
proper  outlet,  and  therefore  fill  the  air  with  the  odor  of  burned 


« 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION        209 

gas  which  is  in  itself  undesirable.  Such  methods  of  warming  a 
room  are  hygienically  bad.  When  heated  air  is  sent  into  a 
room  from  a  furnace  in  the  cellar  it  will  produce  good  ventila- 
tion provided  there  is  some  ready  outlet  for  the  air  of  the  room. 
Heating  a  room  by  a  radiator,  either  hot  water  or  steam, 
simply  warms  the  air  already  present  and  furnishes  no  proper 
outlet  for  the  stale  air,  often  making  the  use  of  special  venti- 
lators a  necessity. 

3.  The  greater  the  difference  in  temperature  between  the 
air  in  a  room  and  that  outside,  the  easier  it  is  to  produce 
currents  of  air.  In  cold  weather  air  comes  in  and  goes  out 
through  cracks  around  doors  and  windows  much  more  rapidly 
than  it  does  in  warm  weather. 

4.  The  rooms  of  an  ordinary  house  are  so  large  in  pro- 
portion to  the  few  people  living  in  them  that  no  attention 
need  be  given  to  ventilation  except  perhaps  in  very  cold 
weather  when  they  are  more  closely  shut. 

5.  Sleeping  rooms  should  be  more  carefully  ventilated 
than  living  rooms.  But  most  care  is  needed  in  schoolrooms 
and  similar  places,  where  many  people  are  gathered  together. 

6.  Expired  air  is  warmer  than  the  ordinary  air  of  a  room, 
and  rises  at  first.  As  it  cools,  however,  it  sinks,  because 
it  is  heavier  than  the  rest  of  the  air  on  account  of  the 
presence  of  carbon  dioxid.  Hence,  while  ventilators  at  the 
top  of  a  room  will  take  away  the  warmed  air,  there  should 
also  be  ventilators  low  down  to  carry  off  the  heavier  gasep 
after  they  have  cooled  and  sunk  to  the  floor. 

Treatment  in  Cases  of  Suffocation. — There  are  many  kinds 
of  accidents  that  result  in  the  exclusion  of  air  from  the  lungs, 
or  asphyxia  as  it  is  called,  producing  suffocation.  In  all  cases 
the  first  thing  to  be  done  is  to  remove  the  cause  of  the  trouble. 
If  it  be  choking  from  compression  at  the  throat,  free  the 
throat  from  whatever  constricts  it;  if  it  be  breathing  poison- 
ous gases,  remove  the  patient  to  fresh  air;  if  it  be  water,  as 
in  the  most  common  cases  of  drowning,  lift  the  patient  by 


210  ADVANCED  PHYSIOLOGY 

the  middle  of  Iiis  body  and  allow  the  water  to  run  out  of  hig 
moutL 

Lay  the  patient  on  his  stomach  with  the  head  turned  to  one 
side  so  that  his  mouth  and  nose  are  away  from  the  ground. 
Either  kneel  at  his  side  or  sit  on  his  hips  and  then  place  the 
hands  upon  the  small  of  his  back,  with  the  thumbs  near  the 
spine  and  the  fingers  spread  out  over  the  lower  ribs.  Then 
throw  your  weight  onto  the  hands  for  about  the  time  it  takes  to 
count  three  slowly,  and  then  slowly  swing  yourself  backwards  so 
as  to  release  the  pressure.  After  three  more  counts  repeat  the 
whole  movement.  The  pressure  when  your  weight  is  thrown 
forward  forces  air  out  of  the  patient's  lungs  and  the  release  of 
the  pressure  causes  them  to  fill  again.  This  produces  what  is 
called  artificial  breathing.  Continue  this  process  about  twelvej 
times  a  minute  without  any  pauses.  Do  not  be  discouraged  foi 
an  hour  at  least.  Pause  occasionally  to  see  if  natural  respirj 
tion  has  started,  by  holding  some  light  object  in  front  of  the 
nostrils.  If  there  is  any  motion  showing  natural  breathingj 
cease  the  artificial  respiration  and  wrap  the  patient  warmly.^ 

THE  VOICE 

While  the  tongue  is  popularly  associated  with  the  voice] 
it  is  really  only  an  agent  which  modifies  sounds  made  neai 
the  entrance  to  the  windpipe.  It  would  be  possible  for  om 
to  make  himself  perfectly  understood,  even  if  his  tongue  were 
removed.  The  words  spoken  by  such  an  individual  woul( 
be  badly  pronounced,  but  just  as  loudly  and  nearly  as  intel-j 
hgibly  as  those  spoken  by  a  normal  person. 

The  Larynx.  — The  voice  box,  or  larynx,  as  it  is  technically] 
called,  is  located  just  below  the  glottis  in  the  trachea;  Fig. 
The  whole  trachea  is  supported  by  incomplete  rings  of  carti-j 
lage,  but  in  the  larynx  region  they  are  especially  formed  toj 

*  If  practical,  demonstrate  this  process  of  artificial  respiration  upon  sora€ 
person  in  the  presence  of  the  class. 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       211 


lake  the  framework  of  the  organ  of  voice.     Their  arrange- 
ient  there   is   as   follows: 

The  uppermost  cartilage,  the  thyroid,  a  broad  U-shaped 
irtilage,  Hes  horizontally  with  the  opening  at  the  back;  its 
mt  curve  protrudes  and  is 
It    through   the     skin     as 

"Adam's  apple";   Fig.    105. 

The  tips  of  the  sides  of  the 

U  at  the  back  have   short 

vertical   growths    on   them, 

one  extending  upward  and 
L^f  ne  downward  on  each  arm 
IK  the  U. 

^^m  Below  the  thyroid  is  the 
^Hricoid  cartilage.  This  is  a 
P^omplete  ring,  narrow  in 
i    front    and    broad     behind. 

Its    lower    hind    border    is 

hinged  on  each  side  to  the 

lower  prongs  on  the  thyroid; 

Fig.  105.    On  the  upper  edge 

of  the   hind  border  of  the 

cricoid  are  located  the  two 

small,   triangular    arytenoid 

cartilages   shown   in  Figure 

106,  which  represents  a  view 

looking  into  the  larynx  from 

above.     These  four  cartilages  together  with  tendons,  muscles 

and  connective  tissue  make  up  the  voice  box. 

The  passage  through  this  structure  will  be  seen  in  Figures 

106  and  107,  to  be  nearly  closed  by  two  transverse,  curtain- 

Uke  membranes  attached  at  the  back    (one  to  each  arytenoid 

cartilage) ,  along  the  sides,  and  at  the  front  (to  the  thyroid) . 

In  front  these  two  membranes  come  nearly  together,  while 

they  are  separated  at  the  back,  thus  leaving  an  approximately 


Fig.  105. — The  larynx  as  viewed 

FROM  THE  LEFT  SIDE 
Slightly  enlarged. 


212 


ADVANCED  PHYSIOLOGY 


trian;;^ular  opening  for  air  to  go  through  in  ordinary  breathing. 
The  straight  inner  borders  of  these  membranes  next  to  the 
triangular  passages  form  the  vocal  cords. 

Sound  and  Voice. — In  making  a  sound  the  vocal  cords  are 
drawn  very  near  one  another  at  their  posterior  ends,   and  are 

stretched   tightly;   air  is   then 


finffenot'd  ^  Cricoid    ^i'^^' 


Fig 


-Thijroid 
Vocal  Cords 

AS 


forced  through  the  slit  between 
them.  In  this  stretching  oi 
the  cords  several  muscles  are 
concerned.  In  Figure  106  the 
muscles  marked  A  and  B  open 
and  close  the  space  between 
the  vocal  cords  by  moving  the 
arytenoid  cartilages  to  which 
they  are  attached.  The  muscle 
marked  C  will  evidently  loosen 
the  cords.  One  of  the  muscles 
that  tightens  them  is  sliown 
in  the  figure  at  D, 

Essentially  this  same  mech- 
anism for  voice  production  is 
present  in  many  lower  animals, 
e.g.    frogs    and    toads,    dogs, 


106. T  HE     LARYNX 

VIEWED  FROM  ABOVE 
A  part  of  the  membranes  and  muscles 
are  removed  so  as  to  show  the  chief 
muscles  concerned  in  opening  and 
closing  (Muscles  A  and  B)  as  well  as 
those  that  loosen  (Muscle  C)  the  vocal 
cords.  Muscle  D  is  one  of  those  which 
tighten  the  cords.  (Carter) 

sheep,  seals,  etc.     The  song  of 
birds  is  produced  by  a  somewhat  different  structure. 

Since  sound  is  due  to  extremely  rapid  movements  in  the  air, 
how  can  the  vocal  cords  be  set  in  vibration  when  the  air  coming 
from  the  lungs  is  passing  them  in  a  continuous  and  steady  cur- 
rent? The  expiratory  muscles,  i.e.  those  of  the  ribs  and 
abdomen,  certainly  do  not  go  through  2000  contractions  per 
second,  and  thus  send  air  from  the  lungs  in  as  many  little 
*'puffs";  yet  2000  per  second  is  the  rate  of  vibration  in  the  air 
which  is  required  to  produce  some  of  the  higher  tones  a  person 
can  sing.  We  all  do  know,  however,  that  a  blade  of  grass 
or  a  strip  of  paper  drawn  between  the  lips  will  vibrate  very 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION        213 

rapidly  even  though  one  blows  on  it  steadily.  For  similar 
reasons  the  vocal  cords,  stretched  across  the  trachea,  will 
vibrate  when  a  strong,  steady  current  of  air  is  sent  through 
them,  thus  producing  air  waves  which  give  rise  to  sound. 

Pitch  of  Voice. — The  short  strings  on  a  piano  give  out 
higher  tones  than  the  longer  ones;  but  the  pitch  of  any  of  the 
strings  may  be   made  higher  by  tightening  them.     In  the 


Cartilage 


Vocal  Cords 

Talkinc] 


Vocal  Cords 

Breaihinq 


Fig.  107. — The  larynx  as  viewed  from  above  with  the  membranes 

in   position 

The  figure  at  the  left  shows  the  vocal  cords  tightened  to  produce  a  sound  as  in  talking 
and  that  at  the  right  shows  them  slackened  and  widely  open  as  in  quiet  breathing. 

larynx,  the  length  of  the  vocal  cords  cannot  be  changed,  so 
pitch  must  be  modified  by  varying  their  tension.  If  the 
muscles  that  tighten  the  vocal  cords  contract,  the  cords  will 
give  out  a  high  tone;  if  these  muscles  relax  a  little  and  the 
opposite  muscles  (Fig.  106)  shorten,  the  vocal  cords  will 
loosen  and  a  lower  tone  result.  Under  ordinary  circum- 
stances these  differences  in  tension  are  brought  about  in- 
voluntarily, but  in  singing,  conscious  determination  of  theii 
tension  occurs  to  a  certain  extent. 

Difference  in  Voice  in  Women  and  Men. — The  reason  why 
the  voice  in  women  is  so  much  higher  in  pitch  than  it  is  in 
men,  is  that  a  woman's  larynx  is  actually  smaller  than  a  man's. 
When  a  boy  is  about  fifteen  years  of  age,  his  larynx  begins  tc 


214  ADVANCED  PHYSIOLOGY 

enlarge,  and  he  goes  through  an  experience  called  a  ^'change 
of  voice";  at  the  close  of  this  period  the  larynx  assumes  its 
permanent  shape  and  size,  and  the  voice  remains  practically 
the  same  thereafter. 

Quality  of  Voice. — The  difference  in  the  "  sound  "  of  the 
voice  in  different  people  is  due  to  the  shape  and  size  of  various 
air  spaces  associated  with  the  throat,  mouth  and  nose.  The 
strings  taken  from  the  finest  violin  in  the  world  and  stretched 
from  one  nail  to  another  in  a  board  would  not  give  out  pleas- 
ing sound,  however  they  were  bowed.  In  like  manner,  air  in 
a  barrel  changes  the  "  sound  "  of  the  natural  voice  when  one 
speaks  into  it;  speaking  into  bottles  of  different  sizes  gives 
rise  to  different  sounds.  The  fine  tone  of  an  instrument  is 
due  more  to  the  vibration  of  the  air  inside  it  than  to  the 
strings  themselves. 

In  the  same  way  the  character  of  the  voice  is  largely  de- 
termined by  certain  air  spaces;  by  the  columns  of  air  in 
the  trachea,  in  the  pharynx  and  in  the  nasal  passages;  by 
certain  air  cavities  in  the  bones  between  the  pharynx  and 
the  brain,  and  by  others  in  the  bones  making  up  the  parti- 
tion between  the  nasal  passages  and  the  brain;  Fig.  96. 

These  spaces  are  all  of  much  consequence  in  determining  the 
finer  characteristics  of  the  singing  voice,  and  much  of  voice 
training  consists  in  developing  the  habit  of  "placing"  the  voice 
in  such  a  way  as  to  obtain  the  best  use  of  these  air  chambers. 

Loudness  of  Voice. — The  loudness  of  the  voice  is  due  to 
the  amount  of  air  and  the  force  with  which  it  is  driven  through 
the  slit  between  the  vocal  cords.  A  piano  string  which  is  set 
in  vibration  by  a  very  forcible  stroke  gives  out  a  loud  sound; 
struck  lightly,  the  same  string,  vibrating  through  lesser  dis- 
tances, gives  out  a  fainter  sound  though  of  the  same  pitch. 
In  a  similar  way,  the  loudness  of  the  voice  depends  upon  the 
amount  of  the  vibration  of  the  vocal  cords,  which  in  turn  is 
determined  by  the  strength  of  the  air  current. 

Pronunciation  is  effected  almost  entirely  by  the  ishaping  of 


MECHANISM  AND  CHEMISTRY  OF  RESPIRATION       215 

the  mouth  and  by  the  use  of  the  lips  and  tongue.  The  lips 
govern  all  sounds  involving  m,  b  and  p,  the  teeth  and  tongue 
sounds  involving  d,  I,  n  and  t;  while  the  tongue,  by  its 
position  at  back  or  front,  governs  to  some  extent  the  pro- 
nunciation of  every  word  one  utters. 

The  readiness  with  which  one  makes  himself  understood 
is  dependent  more  upon  the  clearness  of  his  enunciation 
than  upon  the  loudness  of  his  voice.  Some  public  speakers 
shout  very  loudly  and  yet  are  difficult  to  understand;  others 
speak  quietly,  but  are  heard  easily.  The  difference  is  largely 
due  to  the  degree  of  distinctness  with  which  they  pronounce 
the  consonants  at  the  beginnings  and  endings  of  words.  The 
loud  shouting  of  the  vowel  sounds  renders  one's  voice  less, 
rather  than  more  inteUigible.  If  one  pays  a  little  attention 
to  the  proper  enunciation  of  the  consonant  sounds  he  will 
have  no  difficulty  in  being  understood  either  in  public  speak- 
ing or  private  conversation. 


CHAPTER  XIV 
THE  EXCRETORY  SYSTEM 

No  machine  has  ever  yet  been  invented  so  perfect  in  con- 
struction that  it  will  not  wear  out.  Often  it  is  impossible  to 
see  with  the  naked  eye  the  material  which  wears  away  from 
a  machine,  but  we  know  that  it  does  disappear.  The  axles  of 
wagon  wheels  grow  smaller,  the  tires  wear  away,  bolts  get 
loose;  all  these  parts  have  to  be  renewed  occasionally. 

Furnaces  do  not  show  the  same  kind  of  friction  as  axles  and 
wheel  tires  but  they  require,  at  times,  new  piping,  grates  and 
valves.  In  furnaces,  too,  there  is  another  kind  of  material 
which  must  constantly  be  removed:  the  ashes,  which  are  the 
waste  from  the  burned  fuel,  must  be  raked  out,  or  the  fire- 
box will  become  clogged  so  that  the  fire  will  not  burn.  From 
the  burning  fire,  too,  a  quantity  of  waste  gas  goes  off  up  the 
chimney. 

In  similar  ways,  wastes  are  produced  in  the  human  body. 
The  tissues  are  constantly  wearing  out,  and  the  parts  worn 
away  are  useless  and  must  be  removed. .  In  the  body,  too, 
the  oxidation  of  food  leaves  waste  material  corresponding 
in  a  way  to  ashes,  and  in  this  oxidation  gases  are  produced, 
and  considerable  water.  All  of  this  waste  must  be  eliminated, 
and  the  general  process  of  getting  rid  of  it  is  called  ex- 
cretion. 

EXCRETORY  ORGANS 

These  wastes  are  conveyed  to  the  exterior  by  four  main 
paths:  the  lungs,  intestine,  kidneys  and  the  skin.  It  is  difficult 
to  say  which  is  the  most  important,  for  interference  with  the 
functions  of  any  one  produces  serious  consequences,     Deaths 

?I0 


THE  EXCRETORY  SYSTEM  217 

from  lung  and  kidney  troubles  are  frequent.  Death  from 
skin  troubles  rarely  occurs,  since  the  skin  is  not  apt  to  be 
attacked  over  the  whole  body  at  once,  but  it  has  been  dis- 
covered that  if  a  person's  body  is  painted  over  with  a  varnish 
that  interferes  with  skin  functions,  death  will  inevitably 
result.     (See  "Body  Temperature,"  Chapter  XV.) 

When  we  speak  of  the  portion  of  the  waste  material  ex- 
creted through  the  intestine,  we  do  not  refer  to  the  undigested 
parts  of  the  food  that  simply  pass  through  to  be  discharged, 
but  to  materials  actually  excreted  from  the  body  into  this 
part  of  the  digestive  tract.  Most  of  these  come  from  the 
hver,  which,  as  we  have  seen,  pours  quantities  of  bile 
into  the  intestine.  This  bile  aids  somewhat  in  digestion, 
but  is,  after  all,  chiefly  a  waste  product  which  passes  from 
the  body  with  the  faeces. 

Agency  of  the  Blood  in  Removing  Wastes. — In  the  building 
and  economy  of  any  great  city  two  systems  of  piping  are  con- 
nected with  every  house,  and  are  at  the  service  of  every  in- 
dividual: the  water  pipes  which  supply  the  fresh  water,  and 
the  sewers  which  take  away  the  waste  and  the  polluted 
water.  To  be  sure,  water  could  be  taken  from  a  well  in  the 
cellar  of  each  house,  and  the  waste  could  be  poured  on  the 
ground  outside;  but  these  practices,  sooner  or  later,  would 
almost  certainly  cause  diseases,  if  not  death,  in  the  house  or 
community.  All  up-to-date  houses  are  provided  with  special 
water  supplies  and  sewage  outlets. 

In  the  human  body  the  same  system  of  tubes  serves  to 
bring  in  fresh  food  and  water  supplies  and  to  take  away  the 
wastes.  The  blood,  which  serves  both  these  ends,  is  thus  a 
very  complex  liquid.  It  contains  all  of  the  food  absorbed 
from  the  intestine,  and  in  its  circulation  it  receives  all  the 
wastes  from  the  various  parts  of  the  body,  carrying  them 
away  to  the  organs  that  are  to  excrete  them.  Living  involves 
such  constant  activity  that  waste  matters  are  continually 
thrown  into  the  blood.     A  certain  amount  of  blood  can  ab- 


218  ADVANCED  PHYSIOLOGY 

sorb  only  a  certain  amount  of  these  wastes,  but  if  they  can 
be  constantly  removed  from  it,  the  blood  may  go  on  absorb- 
ing them  continually.  A  part  of  these  materials,  we  have 
already  learned,  is  excreted  through  the  lungs,  since  there 
carbon  dioxid  gas  and  water  are  being  constantly  ehminated, 
respiration  thus  being  in  part  an  excretion.  The  wastes  ex- 
creted through  the  skin  will  be  considered  in  a  special  chapter. 
The  portion  secreted  through  the  kidneys  will  be  noticed  here. 

UREA:    ITS  SOURCE  AND  EXCRETION 

Proteid  food  contains  nitrogen;  therefore,  among  the  body 
wastes  there  must  be  some  which  hold  this  element.  The 
main  one  is  urea,  which  is  essentially  broken  down  proteid 
material,  with  the  chemical  formula  (N2H4)  CO.  Although 
muscles  are  largely  proteid  this  does  not  necessarily  mean 
that  muscular  work  will  result  in  a  large  amount  of  urea 
formation,  for  the  energy  of  muscular  contraction  comes 
chiefly  from  the  oxidation  of  starches,  sugars  and  fats;  since 
these  contain  no  nitrogen  their  oxidation,  of  course,  produces 
no  urea.  A  considerable  quantity  of  urea  does  come  from 
the  muscles,  but  this  happens  whether  they  are  working  or 
not;  for  the  very  act  of  living  results  in  the  breaking  down  of 
proteid  material,  and  consequently  in  nitrogenous  waste. 

The  waste  from  muscles  does  not  leave  them  as  urea,  but 
in  a  slightly  different  form.  It  is  probably  carried  by  the  blood 
to  the  liver,  where  it  is  changed  into  urea.  Thus  we  learn  of 
another  function  of  the  liver,  viz.  in  converting  this  waste 
from  the  form  in  which  it  leaves  the  muscles  into  a  form  ca- 
pable of  excretion.  The  proof  of  this  fact  is  that  an  animal 
from  which  the  liver  has  been  removed,  or  in  which  it  is 
diseased,  gives  off  very  little  urea,  though  an  unusual  amount 
of  ammonia,  which  also  contains  nitrogen,  is  excreted  in 
such  a  case.  From  the  liver  the  urea  passes  into  the  blood 
again,  to  be  carried  to  the  kidneys  whose  function  it  is  tp 
remove  urea  from  the  blood. 


Tiffi  EXCRETORY  SYSTEM 


2id 


The  necessity  for  urea  excretion  is  shown  by  the  fact  that 
all  animals,  even  microscopic  ones,  have  organs  for  its 
removal ;  although  these  organs  are  known  by  different 
names,  in  all  cases  they  correspond  in  function  to  the 
human   kidneys. 


M 


THE  KIDNEYS 

The  kidneys  are  located  one  on  either  side  of  the  body,  in 
the  "small"  of  the  back,  a  little  to  each  side  of  the  backbone 
and  a  trifle  below  the  eleventh  pair  of  ribs,  the  left  kidney 
lying  somewhat  higher  up  than 
the  right;  Fig.  108.  The  peritoneal 
hning  of  the  body  cavity,  is 
stretched  tightly  over  them. 
They  are  firm  in  texture  and 
dark  red  in  color.  Figure  108 
shows  each  kidney  to  be  oval  in 
general  shape  with  a  depression 
on  the  side  toward  the  backbone, 
thus  having  a  form  known  as 
"kidney  shape."  From  the  de- 
pression a  tube,  the  ureter,  leaves 
the  kidney  and  extends  down- 
ward to  the  bladder.  Close  by 
the  exit  of  the  ureter  the  renal 
artery  enters  the  kidney  and  the 
renal  vein  leaves  it. 

The  internal  structure  of  a  kidney  appears  somewhat  as 
in  Figure  109.  The  ureter  is  large  like  a  funnel  as  it  leaves 
the  organ  and  is  continuous  with  a  space,  called  the  pelvis,  in 
he  body  of  the  kidney  itself.  Protruding  from  the  kidney 
substance  into  the  mouth  of  this  funnel  are  conical  structures 
of  soft  tissue,  eight  to  eighteen  in  number,  called  the  Mai- 
pighian  pyramids.     On  the  apices  of  these  are  the  openings 


Bladder 


.Urethra 


Fig.  108. — Diagram 

Showing  the  position  of  the  kidneys 
and  their  connections. 


5!20 


ADVANCED  niYSIOLOGY 


of  numerous  tubules,  which  come  from  the  outer  layer  of  the 
kidney,  the  cortex.  The  outer  ends  of  the  tubules  are  the  real 
glands,  which  produce  the  kidney  secretion;  their  inner  ends 

drain     these     glands, 


Medulla 


Corfei 


^alpiqhian 


Ureter 


carrying  their  secre- 
tion to  the  pyramids 
and  pouring  it  into 
the  funnel-like  open- 
ing of  the  ureter, 
whence  it  runs  to  the 
bladder.  To  under- 
stand the  structure 
and  action  of  the  kid- 
neys we  must  study 
these  tubules  more 
minutely. 

A  Urinary  Tubule. — 
In  Figure  110  a  dia- 
gram of  the  arrange- 
ment of  two  urinary 
tubules  is  given.  Each 
begins  at  its  outer 
end,  i.e.  the  end  to- 
ward the  kidney  surface,  in  the  form  of  a  bulb-like  expansion,  the 
walls  of  which  are  only  one  cell  thick.  This  bulb,  the  Malpighian 
capsule,  is  deeply  indented  on  one  side,  so  as  to  form  a  pocket. 
From  this  pocket,  there  arises  a  long  tube  which  takes  a  some- 
what irregular  course.  It  turns  toward  the  center  of  the  kidney, 
but  almost  at  once  becomes  twisted  into  irregular  coils, 
called  the  convoluted  part  of  the  tube.  Afterwards,  it  pro- 
ceeds in  a  fairly  straight  line  toward  the  pelvis  of  the  kidney, 
but  goes  only  a  short  way,  when  it  turns  sharply  on  itself  and 
returns  toward  the  outer  surface  of  the  kidney  once  more, 
near  where  it  started.  Here  it  is  joined  by  other  tubules  of 
the  same  sort  and  together  the  united  tubes  now  pass  as  « 


Fig.  109. — Representing  a  kidney  opened 
lengthwise 

(Sappey) 


THE  EXCRETORY  SYSTEM 


221 


/vj  lialplqhian 
)  Capsule 

Convoluted  portion 
of  Tube 


single  duct  in  a  nearly  straight  line  to  the  tip  of  one  of  the 
pyramids.  There  the  contents  are  emptied  into  the  pelvis, 
whence  they  immediately 
enter  the  ureter.  Cor-f-ex. 

The  Renal  Blood  Ves- 
sels.— The  distribution  of 
the  blood  vessels  aids  us  in 
understanding  how  these 
tubules  act.  The  artery 
enters  the  kidney  at  the 
pelvis,  and  breaks  up  into 
many  small  vessels  w^hich 
run  toward  the  surface  or 
cortex  of  the  kidney.  Here 
a  minute  twig  enters  each 
of  the  little  pockets  at  the 
beginnings  of  the  tubules 
(Fig.  110),  inside  which 
it  breaks  up  into  a  roundish 
knot  of  capillaries  called  a 
glomerulus.  After  flowing 
through  the  capillaries  the 
blood  emerges  from  the 
pocket  as  a  tiny  vein,  but 
does  not  immediately  flow 
out  of  the  kidney.  A  part  of  it  enters  at  once  another  set  of 
capillaries  that  run  among  the  convoluted  kidney  tubules. 
After  traversing  this  second  set  of  capillaries,  the  blood  enters 
definite  veins  and  flows  out  of  the  kidney  by  the  renal  vein; 
Fig.  111. 

The  Separation  of  Urea  from  the  Blood. — We  must 
keep  in  mind  that  the  main  nitrogenous  waste,  urea,  is 
made  in  the  liver  from  materials  in  the  blood  and  then 
returned  to  the  blood  stream;  and  that  it  is  only  through 
capillary  walls  that  blood  can  expel  its  waste  or  absorb  n3W 


Outlet  of 
Tubule  into' 
Pelvis  of  Kidney 

Fig.  110. — Diagram 

Showing  the  course  of  two  kidney  tubules. 
(Huxley) 


222  ADVANCED  PHYSIOLOGY 

material.  There  are,  then,  two  places  where  material  from 
the  blood  vessels  can  be  set  free  into  the  tubule;  through  the 
walls  of  the  capsule  which  surrounds  the  glomerulus,  and 
through  the  walls  of  the  convoluted  part  of  the  tubule.  By 
a  series  of  delicate  tests  it  has  been  found  that  water  and 
some  common  salts  in  solution  leave  the  blood  through  the 
walls  of  the  capsule.     Although  this  process  is,   doubtless, 

Malpiqhian 


Tubuk 

Fig.  111. — Showing  the  distribution  of  the  capillaries 
around  a  single  kidney  tubule 

The  blood  capillaries  in  the  capsule  form  a  glomerulus. 

largely  one  of  filtration,  it  is  unlike  ordinary  filtering  through 
paper  in  that  not  all  substances  in  solution  will  pass  through. 
The  cells  of  a  Malpighian  capsule  allow  some  substances  to  go 
through,  while  they  prevent  others.  This,  like  the  absorption 
of  food  through  the  intestinal  walls,  can  only  be  explained 
by  saying  that  the  cells  making  up  the  membranes  are  alive. 

Where  the  capillary  blood  vessels  spread  out  over  the  con- 
voluted part  of  the  tubule,  the  cells  of  the  tubule  are  true 
secreting  cells,  selecting  from  the  blood  waste  organic  ma- 
terials, chiefly  urea,  but  also  some  other  substances  {pig- 
ment, 'phosphoric  and  sulfuric  acids,  sodium,  chlorine,  ammo- 
nia, etc.).  These  pass  into  the  tubule;  there  the  water  coming 
down  from  the  capsule  dilutes  the  secretion  and  carries  it 
into  the  pelvis  cavity. 

The  entire  kidney  is  a  compact  mass  of  thousands  of  these 
tubules,  each  having  an  irregular  course  and  each  opening 
into  the  reservoir  of  the  pelvis.  Inasmuch  as  the  cortex  is 
so  richly  supplied  with  blood  capillaries,  this  surface  layer  is 
redder  in  appearance  than  the  deeper  parts  which  border  on 


THE  EXCRETORY  SYSTEM  223 

the  pelvis.  This  latter  medullary  region  is  made  up  for  the 
most  part  of  larger  blood  vessels,  connective  tissue  and  col- 
lecting tubules. 

The  blood  that  flows  out  of  the  kidney  by  the  renal  vein  is 
the  purest  in  the  body.  It  is  arterial  blood  containing  con- 
siderable urea  when  it  enters,  but  in  flowing  through  the 
kidneys  the  urea  and  some  other  wastes  are  removed,  so  that 
it  flows  out  actually  purer  than  when  it  entered. 

Urine  Excretion. — The  rate  at  which  the  kidneys  excrete 
urine  is  very  variable,  depending  largely  upon  conditions  of 
the  air  one  breathes.  More  is  excreted  in  cold  weather  than 
in  warm,  and  more  in  wet  weather  than  in  dry.  In  hot,  dry 
weather  so  much  of  the  water  waste  of  the  body  leaves  it  in 
the  form  of  perspiration  that  less  is  passed  off  through  the 
kidneys.  Certain  foods  and  drugs,  the  drinking  of  a  great 
quantity  of  water  or  other  liquids,  and  nervousness  are  all 
agents  which  may  alter  the  rate  of  secretion.  The  rate  at 
which  the  urea  is  secreted  is  not,  however,  dependent  upon 
these  factors.  It  is  dependent  simply  upon  the  rate  of  its 
formation  in  the  body.  If  formed  rapidly,  it  is  excreted  rapid- 
ly, even  though  the  total  amount  of  urine  is  small."  The  rate 
of  urea  formation  is  dependent  upon  the  rate  at  which  pro- 
teid  material  is  broken  down  in  the  body,  and  the  kidneys 
will  eliminate  this  urea  as  fast  as  it  is  brought  to  them  by  the 
blood.  An  average  daily  amount  of  kidney  secretion  is  three 
pints. 

The  Ureters. — The  ureters,  which  receive  the  urine  from 
the  kidneys,  are  small  tubes  of  about  the  diameter  of  a  good 
sized  quill.  Internally,  they  are  lined  with  a  mucous  mem- 
brane, outside  of  which  muscles  are  arranged,  essentially 
as  in  the  intestinal  walls.  By  their  peristaltic  contraction 
these  muscles  force  the  urine  downward  into  the  bladder. 

The  Bladder.— The  bladder,  Fig.  108,  is  the  reservoir  for 
the  temporary  storage  of  the  urine,  and  is  located  in  the 
middle  of  the  abdominal  cavitv,  in  front  of  the  rectum.     It 


224  ADVANCED  PHYSIOLOGY 

is  an  oval  sac  and  when  moderately  full  is  about  five  inches 
in  vertical  measurement  and  three  inches  across,  hokUng 
about  two  thirds  of  a  pint.  The  muscle  fibres  of  its 
walls  are  smooth  extending  in  every  direction  about  it,  so 
that  when  they  contract  during  the  process  of  emptying,  the 
bladder  shrinks  in  all  its  dimensions. 

The  Urethra. — The  single  tube  which  leads  from  the  middle 
of  the  lower  end  of  the  bladder  to'  the  exterior,  is  called  the 
urethra.  The  opening  from  the  bladder  into  it  is  ordinarily 
closed  by  strong  circular  muscles  passing  around  the  tube  at 
its  point  of  exit.  These  muscles  stay  in  a  condition  of  con- 
stant, involuntary  contraction  most  of  the  time,  relaxing 
only  on  receipt  of  a  special  message  from  the  b^-ain. 

The  Need  of  Drinking  Fresh  Water. — In  the  chapter  on  foods 
we  learned  that  the  body  needs  a  constant  and  large  supply 
of  water.  The  necessity  for  plenty  of  water  in  dissolving  and 
removing  body  wastes  through  the  kidneys  furnishes  one  of 
the  chief  reasons  for  this.  Most  of  the  water  that  flows  through 
the  kidney  tubules  must  come  originally  from  the  water  we 
drink.  If  plenty  is  supplied,  the  whole  liquid  content  of  the 
blood  can  be  more  easily  kept  in  solution,  and  more  water  can 
be  given  off  in  the  urine  to  "flush"  the  system.  The  sewers 
of  a  city  must  never  be  of  too  small  capacity  and  they  must 
never  become  clogged;  water  must  be  kept  running  abun- 
dantly in  them  to  prevent  solids  from  settling  and  decom- 
posing; otherwise,  pestilence  and  disease  set  in.  Similarly, 
every  organ  and  cell  in  the  body  must  have  plenty  of  liquid 
blood  flowing  through  and  past  it  to  furnish  fresh  supplies, 
and  to  receive  all  the  wastes,  liquid,  solid  or  gaseous. 

GENERAL  SUMMARY  OF  METABOLISM 

Since  urea  represents  the  form  in  which  all  the  nitrogen  of 
the  proteid  material  in  our  food  leaves  the  body,  the  whole 
process  of  metabolism  may  be  appropriately  mentioned  here. 
In  an  earlier  chapter  the  definition  of  the  term  metabolism 


THE  EXCRETORY  SYSTEM  225 

showed  it  to  be  the  series  of  changes  by  which  simple  inorganic 
matter  is  built  up  into  complex  organic  matter,  and  all  the 
consequent  changes  by  which  it  is  broken  down  again  into 
simple  elements. 

With  the  foregoing  study  of  kidney  excretion,  the  story  of 
metabolism  is  nearly  complete.  It  begins  with  the  life  of 
plants  that  take  carbon,  oxygen,  hydrogen  and  nitrogen  from 
simple  gaseous  and  mineral  sources,  and  build  them  up  into 
proteid,  carbohydrate  and  fatty  compounds.  Man,  by  eat- 
ing plants,  converts  these  into  animal  proteids,  carbohydrates 
and  fats.  To  be  sure,  some  of  his  foods  come  directly  from 
other  animals,  but  even  these  come  originally  from  plants. 
After  performing  various  functions  as  animal  tissue  in  the 
body,  food  is  broken  down  and  excreted.  Much  of  it  leaves 
the  body  as  carbon  dioxid  gas  and  water,  reduced  thus  to  the 
condition  in  which  plants  originally  obtained  it.  Part  of  the 
food  leaves  the  body  as  urea  and  part  of  it  remains  in 
the  body.  Later,  the  urea  secreted  as  well  as  the  tissues  of  the 
dead  body  undergo  a  further  set  of  decomposition  changes. 
They  are  attacked  by  a  host  of  microscopic  organisms  (bacteria 
and  molds)  causing  further  and  more  complete  breaking  down. 
These  processes  are  colled  fermentation,  decay  and  putrefaction; 
but  it  should  be  remembered  that  these  are  simply  names 
for  the  final  steps  in  the  decomposition  of  food  materials. 
At  last  they  are  brought  once  more  into  the  same  condition 
as  that  from  which  they  started,  so  that  a  new  generation 
of  plants  can  feed  upon  them.  The  whole  process  is  a  cycle, 
the  same  materials  circulating  around  in  an  endless  succession 
from  soil  and  air  to  plants,  from  plants  to  animals,  from 
animals  back  again  to  the  soil  or  air,  partially  through  the 
agency  of  bacteria,  to  start  again  on  their  round  of  usefulness 


i 


DISEASES  OF  THE  EXCRETORY  ORGANS 

Excretion  of  the  wastes  of  the  body  is  absolutely  necessary, 
anything  interferes  with  the  action  of  the  kidneys,  the 


226  ADVANCED  PHYSIOLOGY 

body  becomes  rapidly  poisoned  by  the  accumulation  of  urea 
in  the  blood. 

Bright's  Disease  is  a  name  which  really  covers  a  number  of 
different  diseases  but  they  are  all  characterized  by  an  inter- 
ference with  the  power  of  the  kidneys  to  excrete  urea  and 
other  wastes.  One  of  the  earliest  symptoms  is  usually  the 
appearance  of  considerable  albumen  in  the  urine.  In  a 
healthy  condition  the  urine  contains  no  albumen  and  its 
appearance  is  always  an  indication  of  faulty  metabolism. 
Although  Bright's  disease  is  dangerous,  recovery  from  certain 
forms  of  it  is  frequent. 

Kidney  Stones. — In  another  disease  of  the  excretory  organs, 
hard,  little  nodules,  called  kidney  stones  or  calculi,  form  in  the 
pelvis  of  the  kidney  and  pass  down  into  the  bladder.  They 
are  apt  to  cause  severe  pains  as  they  go  through  the  ureters 
and  sometimes  cause  alarming  symptoms.  Usually,  if  prop- 
erly treated,  they  do  not  produce  much  trouble,  and  some- 
times they  pass  away  with  the  urine.  In  some  severe 
cases,  however,  a  surgical  operation  is  necessary  for  their 
removal. 

Diabetes  is  the  name  given  to  a  disease  in  which  sugar 
appears  in  the  urine,  the  normal  urine  containing  none.  It 
is  not,  however,  a  disease  of  the  kidneys,  although  the  trouble 
is  detected  in  the  secretion  from  these  organs.  It  is  due 
rather  to  improper  nutritive  processes  in  the  body,  although 
the  exact  seat  of  the  trouble  has  not  yet  been  determined. 
An  individual  suffering  from  this  disease  is  unable  to  assimi- 
late his  foods  properly  and  there  seems  to  be  especial  dif- 
ficulty in  the  assimilation  of  sugar.  This  results  in  an 
excessive  amount  of  such  material  in  the  system  and  the 
kidneys  are  obliged  to  excrete  it.  Diabetes  is  a  very  serious 
disease,  and  recovery  from  it  is  rare. 

Jaundice  is  a  term  used  to  denote  symptoms  of  some 
derangement  of  the  liver,  because  of  which  it  is  failing  to 
carry  on  its  proper  functions  in  connection  with  excretion. 


THE  EXCRETORY  SYSTEM  227 

'  The  actual  cause  is  not  known,  but  the  symptoms  are 
striking.  The  disease  is  characterized  by  a  noticeable  yellow 
hue  of  the  skin  and  very  dark  urine.  The  colors  are  some- 
times so  deep  as  to  be  alarming,  but  the  trouble  is  not  serious 
as  a  rule,  and  soon  disappears.  The  real  cause  of  none  of  these 
several  diseases  is  as  yet  known.  They  do  not  seem  to  be 
produced  by  disease  germs,  and  none  of  them  are  contagious. 
No  methods  of  avoiding  them  are  known  beyond  the  general 
one  of  maintaining  good  health  by  proper  exercise  and  diet, 
avoiding  overeating  and  stimulants. 


CHAPTER  XV 

THE  SKIN 

The  skin  is  not  ordinarily  considered  an  organ  of  much 
importance.  It  seems  to  be  merely  a  covering  for  the  body 
and  it  is  not  at  first  easy  to  believe  that  the  skin  actively 
functions.  In  reality,  it  is  an  important  organ  which  performs 
some  of  the  most  vital  offices  in  the  human  body.  There  is 
no  part  of  the  body  which  has  more  to  do  with  one^s  comfort 
than  the  skin;  and  there  is  almost  no  part  whose  sluggish  or 
improper  functioning  leads  to  more  general  unpleasantness  or 
is  more  liable  to  induce  illness. 

STRUCTURE  OF  THE  SKIN 

The  skin  is  a  sheet  of  tissue  covering  every  part  of  the 
surface  of  the  body,  except  the  eyeballs,  and  even  these  when 
the  eyes  are  closed;  there  are  a  few  large  openings  through  it 
for  the  entrance  and  exit  of  solid  matter.  The  skin  is  about 
j^  of  an  inch  thick,  but  it  varies  considerably,  being  much, 
thicker  on  the  soles  of  the  feet  and  palms  of  the  hands  than 
elsewhere.  If  a  thin  section  of  the  skin  is  examined  under  a 
microscope  it  will  be  seen  to  consist  of  two  distinct  layers, 
an  outer  called  the  epidermis,  and  an  inner  called  the  dermis. 
The  epidermis  is  lifeless,  save  for  a  thin  layer  on  its  inner 
surface,  and  can  be  cut  without  pain  or  bleeding;  the  dermis 
is  extremely  sensitive,  full  of  nerves,  blood  vessels  and  glands; 
Fig.   112. 

The  difference  between  a  plump  person  and  a  slender  one  is 
also  manifest  in  the  skin  appearance  generally,  for  m  the  former 
much  fat,  called  adipose  tissue,  is  often  present  among  the  glands 
and  connective  tissue  of  the  dermis. 

22§ 


THE  SKIN 


229 


is  necessary  to  cover  the  body.  If  it  be  seized  by  the  fingers 
almost  anywhere,  e.g.  on  the  back  of  the  hand,  it  can  easily 
be  Ufted  into  a  fold,  but  returns  to  its  original  place  when 


Flattentd 
Cells 


Epidcimk 


Blood 
Vessels 


Dermis 


Qrowlng 
Cell6- 
Blood 
^sseh 

Nerves 


Fig.    112. — Section  through  the  skin 

Showing  the  layers  of  the  epidermis  and  the  sense  organs   and  blood    vessels  of  the 

dermal  papillae. 


released.  On  account  of  this  elasticity  it  readily  accommo- 
dates itself  to  the  shape  of  the  body,  and  is  ordinarily  stretched 
smoothly  over  it.  As  a  person  grows  older,  it  becomes  less 
elastic  and  is  finally  thrown  into  wrinkles. 

THE  EPIDERMIS 

The  inner  surface  of  the  epidermis  is  composed  of  a  layer 
of  growing  cells,  somewhat  rounded  in  shape;  Fig.  112. 
They  are  nourished  by  the  blood  from  below,  and  are  con- 
stantly multiplying  and  growing.  As  they  increase  in  num- 
bers the  new  cells  push  the  older  ones  toward  the  outer  sur- 
face of  the  skin,  and  the  epidermis  is  thus  made  thicker  by 
growth  in  its  deeper  layers.  As  soon  as  the  cells  are  pushed 
away  from  the  deep,  growing  layer,  they  cease  to  have  life 


280  ADVANCED  PHYSIOLOGY 

and  gradually  become  flattened  by  pressure.  The  skin  is 
always  wearing  away  at  its  surface  because  of  the  constant 
friction  it  receives.  Debris  resulting  from  this  wear  is  not 
ordinarily  noticed,  but  when  it  accumulates  in  the  hair, 
along  with  the  dried  secretion  of  certain  skin  glands,  it  is 
called  dandruff.  After  scarlet  fever,  measles,  etc.,  the  epider- 
mis may  come  off  in  sizable  flakes. 

Some  of  the  deeper  cells  of  the  epidermis  contain  pigment 
matter  which  gives  the  skin  its  color.  This  pigment  differs 
in  the  skins  of  different  races;  in  the  negro  it  is  abundant  and 
black;  in  the  yellow  races  it  is  of  a  brownish  yellow  color;  in 
the  skin  of  the  white  races  there  is  very  little,  but  here,  too,  it 
varies  slightly  in  amount,  producing  differences  in  complexion, 
e.g.  blonde  and  brunette.  Freckles  are  due  to  the  unequal 
distribution  of  this  pigment  which  may  be  especially  dense 
in  spots;  they  are  frequently  produced  in  children  by  much 
exposure  to  sunshine  or  cold  winds. 

Thickened  Parts  of  the  Epidermis. — Wherever  there  is 
more  than  the  usual  amount  of  wear,  the  epidermis  grows 
more  rapidly  and  becomes  thicker  than  elsewhere;  examples 
of  this  growth  are  seen  in  the  callouses  on  the  hands  and  feet. 
If  the  rubbing  is  not  severe  but  long  continued,  the  epidermis 
grows  into  prominences  called  corns  or  bunions.  Blisters 
result  from  a  sudden  rubbing  of  the  skin,  the  capillaries  being 
stretched  and  lymph  collecting  between  the  dermis  and  epi- 
dermis in  consequence. 

Skin  Grafting. —  The  only  way  in  which  epidermis  grows 
is  by  multiphcation  of  the  cells  in  its  deeper  layers.  When 
these  growing  cells  are  destroyed  over  a  large  area,  e.g.  after 
severe  burns,  it  may  be  difficult  for  the  epidermis  to  be 
reproduced.  If  a  bit  of  epidermis  is  taken  from  a  healthy 
part  of  the  body,  or  from  some  other  person,  and  firmly 
placed  upon  the  raw  surface  of  such  a  wound,  it  will  generally 
grow  there,  extending  rapidly  and  eventually  covering  the 
surface   which   would   not   otherwise   have   healed.     Such  a 


THE  SKIN 


231 


procedure  is  called  skin  grafting  and  in  modern  surgery  is  a 
common  practice  of  dealing  with  slowly  healing  wounds, 
especially  wounds  from  burns. 

Hair. — To  the  naked  eye  hair  appears  unlike  any  other  part 
of  the  skin.  Throughout  most  of  its  length,  hair  is  dead 
and  shows  little  structure;  but*  near  the  root  where  still 
aUve  it  is  made  of  cells  like  all  other  organic  material.     If  a 


\rferu    \ 

HairPapiUa 

Fig.  113.— Sec- 
tion THROUGH 
THE  BASE  OI-  A 
HAIR 

Showing  its  differ- 
ent layers,  the 
papilla  upon  which 
it  grows  and  the 
blood  vessel  that 
nourishes  it. 


'-ifZjiMusck 


~]^aJt  Ciand 
Fig.  114. — Section  through  the  skin 

Showing    the     various    organs    in    the    dermis    and 
epidermis. 


hair  were  split  and  examined  under  the  microscope,  its  appear- 
ance would  be  something  as  in  Figure  113.  In  the  center  is 
a  kind  of  pith  called  the  medulla  of  the  hair;  next  this  is  a 
horny  layer,  the  so-called  cortex,  in  the  cells  of  which  is  the 
pigment  determining  its  color.  Outside  the  cortical  layer  is 
the  cuticle  of  the  hair,  a  transversely  arranged  series  of  horny 
cells,  each  upper  row  overlapping  the  one  below  it  like  the 
shingles  of  a  roof.     Each  hair  comes  out  of  a  sac,  or  hair 


232  ADVANCED  PHYSIOLOGY 

follicle,  a  tiny  canal  of  epidermal  cells  extending  down  into 
the  dermis;  Figs.  113  and  114.  The  lower  end  of  this  folUcle 
is  enlarged  and  projecting  upward  into  it  is  a  papilla  on  which 
the  hair  grows.  Cells  of  this  papilla  are  constantly  multiply- 
ing and  turning  into  hair  substance  and  thus  the  hair  length- 
ens. After  a  time  (in  the  scalp,  perhaps  three  years),  the  top 
of  the  papilla  ceases  to  form  new  cells,  the  hair  dies  and  falls 
out.  Before  this  occurs,  however,  a  new  papilla  has  been 
budded  off  the  side  of  the  old  one  and  from  it  a  new  hair  starts. 
When  a  hair  is  pulled  out  the  epidermal  cells  lining  the 
follicle  may  come  away  also,  but  the  papilla  usually  remains 
uninjured  and  a  new  hair  soon  grows  from  it.  The  straight- 
ness  or  curliness  of  hair  depends  on  its  shape:  kinky  hair  is 
flat  or  oval  in  cross  section;  wavy  hair  is  oval;  while  straight 
hair  is  round  and  rod-like. 

Emptying  into  each  hair  follicle  is  usually  an  oil  or  sebaceous 
gland;  Fig.  114.  These  glands  secrete  a  substance  which 
moistens  the  surface  of  the  hair  and  keeps  it  soft  and  flexible- 
To  the  lower  end  of  the  follicle  in  most  hair-bearing  animals 
is  fastened  a  slender  muscle,  its  other  end  being  attached  to 
the  lower  layers  of  the  epidermis;  Fig.  114.  The  shortening 
of  this  muscle  pulls  the  follicle  into  a  more  vertical  position, 
making  the  hair  "stand  up  straight,"  as  a  cat's  fur  frequently 
does,  for  example. 

All  epidermal  structures  are  disturbed  and  cast  off  to  a 
greater  or  less  extent  in  the  case  of  some  fevers,  and  not  in- 
frequently the  hair  falls  out  after  a  long  sickness. 

Hair  itself  is  not  sensitive,  though  if  it  is  stiff  one  may  feel  a 
very  slight  touch  upon  it  becauseof  the  presence  of  nerves  in  the 
dermis  at  its  base.  The  stiff  hairs  around  the  nostrils  of  a  cat 
are  thus  sense  organs  of  touch.  Over  most  of  the  human  body, 
hair  remains  so  short  as  to  be  almost  invisible  and  of  only 
slight  protective  value.  The  tendency  for  hair  to  fall  out  and 
leave  the  head  bald  is  probably  due  in  part  to  the  bad  habit  of 
vvearing  hot,  heavy  hats  with  stiff  rims  which  bind  the  scalp. 


THE  SKIN 


233 


Nails. — The  finger  and  toe  nails  are  especially  thickened 
(parts  of  the  epidermis.  Figure  115  represents  a  lengthwise 
[section  through  the  tip  of  the  finger,  showing  a  nail.  It 
grows  chiefly  at  its  base,  called  the  root,  and  as  it  grows 
its  free  end  is  pushed  out  farther  and  farther.  It  also 
grows  thick  by  additions  to  its  un- 
der surface.  The  reason  why  a  nail 
appears  whiter  at  its  basal  end  is 
that  blood  capillaries  are  less  plentiful 
in  that  region  than  elsewhere;  this 
*'white"  of  the  nail  is  technically 
called  the  lunula. 


f^' ■l^oi'Mn 


Fig.      115. — Section 
through  the  end  op 

A  FINGER 

Showing   the     relation     of 

the  nail  to  other  parts. 


THE  DERMIS 

Below  the  epidermis  is  a  live  layer 
composed  of  connective  tissue,  nerves, 
blood  vessels  and  fat.  It  is  largely 
made  of  a  dense  mass  of  connective 

tissue  fibres  like  the  material  we  have  already  noticed 
in  tendons  and  ligaments,  except  that  in  skin  it  is  arranged 
in  a  much  looser  mass;  the  fibres  run  in  every  direction,  are 
closely  packed  together  near  the  epidermis,  but  below,  near 
the  muscles,  become  quite  loose;  Fig.  114.  In  the  spaces 
between  the  fibres  are  masses  of  fat  cells  which  fill  out 
the  skin  and  make  the  body  appear  rounded.  If  these  layers 
of  fat  were  not  there,  the  skin  would  cling  tightly  to  the 
flesh  so  that  muscles  and  tendons  would  show  through  it. 
When  a  person  is  insufficiently  nourished,  as  for  example  after 
a  long  illness,  the  location  of  the  separate  muscles  beneath 
the  skin  is  plainly  seen  because  the  fat  stored  in  the  dermis 
has  been  used. 

The  dermis  is  full  of  blood  vessels.  This  is  most  evident  on 
certain  areas,  e.g.  the  lips  and  inner  surfaces  of  the  eyelids, 
where  the  epidermis  is  very  thin  and  the  capillaries  of  the 
dermis  show  through,  giving  these  areas  their  red  appearance. 


234 


ADVANCED  PHYSIOLOGY 


Cold  Perceimq  Areas 


The  outer  surface  of  the  dermis,  where  it  comes  into  con- 
tact with  the  epidermis  is  not  flat  and  smooth  but  shows 
many  small   elevations,    called   papillae;    the   epidermis    fits 

over  these  so  that  the  two 
layers  dovetail  into  each 
other;  Fig.  112.  These 
papillae  on  certain  parts 
of  the  body,  e.g.  on  the 
palms  of  the  hands,  are 
arranged  in  parallel  or 
concentric  rows  so  that 
they  show  through  the 
epidermis  and  produce 
the  fine  lines  which  appear 
on  the  tips  of  the  fingers 
and  toes. 

Organs  of  Touch,  Heat 
and  Cold. — In  these  pa- 
pillae, nerve  endings 
and  blood  vessels  are 
abundant,  though  the 
same  papilla  does  not 
usually  contain  both. 
Some  nerve  endings  as- 
sociated with  touch  and 
temperature  changes  are 
shown  in  Figure  112.  A 
number  of  endings  in  the 
same  region  will  perceive 
only  cold,  others  only 
warmth;  so  that  in  general  we  may  say  that  the  whole 
body  is  mapped  out  into  "  cold  and  warm  spots  ";  Fig.  116. 
The  ends  of  nerves  which  are  sensitive  to  touch  are  called 
tactile  corpuscles  or  end  bulbs;  Figs.  117  and  118.  They  are 
of  different  shapes  and  extremely  small,  varying  for  the  most 


Warmth  Perceimq /trea$ 


Fig.  116. — Diagram 

Showing  the  areas  on  the  back  of  the  hand 
that  perceive  heat  and  cold.  The  two  figures 
represent  the  same  area,  one  figure  showing 
the  cold  and  the  other  the  heat  perceiving 
areas.  (Goldschneider) 


£ncfBufb 


Fig. 


117. — One  op  the  end 
of  touch  in  the  eye 

(Dogiel) 


^ervc- 


BULBS 


THE  SKIN 


235 


part  from  ^l-^j  to  -g-J-g-  inch  (0.04-0.08  mm.)  in  diameter. 
The  sense  of  touch  may  be  one  of  mere  pressure,  or  when 
excessive  may  be  that  of  pain.  Naturally, 
those  parts  of  the  body  are  most  sensitive 
where  the  papillae  which  contain  these 
nerve  endings  are  most  numerous.  The 
tip  of  the  tongue  has  the  most  nerve 
endings  to  a  given  area,,  and  the  finger 
tips  are  the  next  most  sensitive  organs. 
Nerve  endings  are  farthest  apart  on  the 
back,  and  on  the  back  of  the  neck. 
Two  points  one  tenth  of  an  inch  (2.5 
mm.)  apart  can  be  identified  as  two  if 
they  are  on  the  finger  tips.  In  the  middle 
of  the  back,  however,  two  points  two 
and  a  half  inches  (66  mm.)  apart  may 
be  felt  as  one. 


Fig.  118. — A  tactile 

CORPUSCLE  FROM 

THE     FINGER 
(Ruffini) 


The  Skin  as  a  Protecting  Organ. — The  skin  is  a  protection 
against  the  entrance  of  disease  germs.  The  many  over- 
lapping layers  of  epidermis  cells  form  such  a  thick  mass  that 
bacteria  cannot  penetrate  it  and  reach  the  living  parts  within. 
If  it  is  broken,  however,  bacteria  can  attack  it  at  once.  The 
need  of  thoroughly  cleansing  skin  wounds  is  thus  manifest. 

Any  of  the  common  antiseptic  washes  or  lotions  are  of  some 
value,  but  especially  those  containing  formalin  (3-10%  is  very 
effective),  bichloride  of  mercury  (1  part  in  1000),  or  carbolic 
acid  (23^%),  are  effective,  easily  used,  and  inexpensive.  If  cer- 
tain treatments  cause  sharp  pain  for  a  few  minutes,  this  is  a 
good  indication,  for  it  probably  means  that  the  naked  tissue  is 
being  killed,  with  the  bacteria  on  it. 

THE  SKIN  AS  AN  EXCRETING  ORGAN 


The  skin  secretes  perspiration  at  the  rate  of  one  to  five 
pints  per  day.     This  quantity  varies  according  to  the  amount 


236 


ADVANCED  PHYSIOLOGY 


'^=-(^^^^idermii 


of  exercise  a  person  takes  and  the  condition  of  the  air  about 
him.  One  perspires  less  on  a  wet  day  than  on  a  dry  one,  and 
less  in  cold  weather  than  in  warm.  Ordinarily  this  secretion 
is  produced  so  slowly  that  it  evaporates  as  fast  as  it  is  formed 
and  except  for  a  realization  that  the 
skin  is  kept  moist  and  flexible,  one  is 
unconscious  of  it.  When  the  glands 
secrete  very  rapidly,  their  output  may 
not  evaporate  as  fast  as  it  is  formed, 
and  collects  in  small  drops;  this  occurs 
particularly  when  the  weather  is  hot,  or 
when  one  is  exercising  vigorously.  Phy- 
siologists speak  of  this  ''sweat"  as  sensi- 
ble 'perspiration,  while  the  ordinary  slow 
secretion  is  called  insensible  perspiration. 
The  amount  of  insensible  perspiration 
increases  with  a  rise  in  temperature, 
from  a  cold  state  up  to  about  92 °F;  a 
very  sudden  increase  in  the  perspiration 
rate  then  sets  in,  and  sweat  drops  collect 
on  the  skin;  at  the  same  time,  CO2  is 
eliminated  in  considerable  amount 
through  the  skin.  In  this  connection  it 
is  interesting  to  note  that  in  some  ani- 
mals, e.  g.  the  earthworm,  frog,  etc.,  the 
skin  is  the  principal  breathing  organ. 

Sweat  Glands. — There  are  about  two 
and  a  half  million  sweat  glands  scat- 
tered through  the  dermis  of  the  human 
body.  They  occur  in  least  numbers  in  the  middle  of  the 
back,  where  there  are  about  four  hundred  per  square  inch, 
while  on  the  palm  of  the  hand  and  sole  of  the  foot  there  may 
be  two  thousand  five  hundred  in  the  same  area.  Each  sweat 
gland  is  a  minute  tube  of  uniform  diameter,  closed  at  its  inner 
end  where  much  of  its  length  is  coiled  into  a  knot;  Fig.  119. 


Fig.      119. — Diagram 

Showing  a  sweat  gland,  its 
duct  and  its  blood  supply^ 


THE  SKIN  237 

The  cells  which  constitute  this  part  of  the  tube  are  the  true 
secreting  cells,  and  this  glandular  portion  is  surrounded  by 
a  net-work  of  blood  capillaries.  The  ducts  from  different 
glands  do  not  join  one  another,  but  each  passes  nearly  straight 
up  through  the  dermis,  then  through  the  epidermis  in  a  wavy 
course,  to  open  by  a  minute  pore  on  the  surface  of  the  skin. 
The  pores  are  too  small  to  be  seen  with  the  naked  eye,  but 
are  easily  visible  if  the  skin  is  examined  with  a  good  lens. 

Like  the  other  glands  in  the  body  sweat  glands  are  under 
the  control  of  definite  nerve  fibres,  called  secretory  nerves. 
These  are  stimulated  by  various  means;  by  reflex  influences 
when  strenuous  muscular  work  is  being  performed;  by  the 
condition  of  the  surrounding  air;  by  fright  or  by  special  con- 
ditions of  the  internal  organs.  Like  other  glands,  too,  their 
action  is  not  within  control  of  the  will. 

Functions  of  the  Sweat  Glands.— The  sweat  glands  have 
two  very  important  functions:  (1)  Excretion  of  water  and 
other  materials.  Large  amounts  of  perspiration,  which  is 
water  in  great  measure,  are  secreted  daily,  thus  making  the 
skin  second  only  to  the  kidneys  in  regulating  the  amount  ol 
water  in  the  blood.  There  are  also  small  amounts  of  various 
salts,  traces  of  fat  and  other  substances  in  perspiration.  If 
on  account  of  a  disease  of  the  kidneys,  urea  cannot  be  properly 
excreted  from  them,  it  may  be  partially  disposed  of  through 
the  skin,  which  thus  helps  to  purify  the  blood.  (2)  Regula- 
tion of  body  temperature.  This  is  a  matter  of  such  importance 
that  it  must  be  discussed  in  considerable  detail. 

BODY  TEMPERATURE 

The  life  processes  in  all  animals  and  plants  are  closely 
related  to  temperature.  At  the  freezing  point  all  their 
activities  stop;  at  temperatures  sHghtly  above  this  they  begin 
and  with  increase  of  temperature  become  more  vigorous. 
For  the  human  body  98°  F.  seems  to  be  a  very  favorable  tem- 
perature.    Even  the  simple  functions  of  digestion  are  checked 


238  ADVANCED    PHYSIOLOGY 

by  temperatures  markedly  lower  or  higher  than  this;  and  it 
follows,  therefore,  that  the  greatest  vigor  is  possible  only 
when  the  body  is  warm. 

Not  only  is  the  body  warm  but  it  is  kept  at  an  almost  uni- 
form temperature.  This  varies  slightly  in  different  persons, 
and  in  the  same  person  different  parts  of  the  body  show  slight 
variations  from  the  average  of  98.6°  F.  The  internal  organs 
are  considerably  warmer  than  those  on  the  surface;  the  tem- 
perature of  the  skin  itself  is  not  much  over  90°  F.,  while  that 
of  the  liver  may  be  as  high  as  107°  F.  Moreover,  the  body 
heat  differs  a  little  from  hour  to  hour,  being  greatest  between 
1  P.  M.  and  4  P.  M.  and  least  between  1  A.  M.  and 
4  A.  M. 

Health  is  so  dependent  upon  the  maintenance  of  proper 
body  temperature  that  if  there  is  much  departure  from  the 
normal,  illness  results.  If  the  temperature  rises  to  over 
100°  F.  we  say  that  the  individual  concerned  has  a  fever;  a 
slight  fall  of  temperature  below  98°  F.  is  an  equally  sure 
indication  of  illness,  though  we  have  no  special  name  for  this 
condition  and  less  commonly  hear  about  it.  During  a  high 
fever  a  person's  temperature  may  rise  to  106  F.  or  even  a 
little  higher,  and  recovery  take  place,  but  a  rise  to  107°  F. 
or  108°  F.  is  usually  followed  by  death. 

The  source  of  all  body  heat  is  the  oxidation  of  foods.  All  body 
activity  involves  the  oxidation  of  food  or  tissues,  and 
thus  is  necessarily  accompanied  by  heat  production.  This 
explains  why  we  get  warm  when  exercising  vigorously,  why 
we  like  to  move  around  quickly  on  a  cold  day,  and  why  we 
need  extra  clothing  when  not  exercising.  We  must  not,  how- 
ever, confuse  feeling  cold  with  being  cold.  On  a  cold  winter  day 
one  feels  much  colder  than  on  a  warm  summer  one,  and  it  is 
hard  to  believe  that  the  body  temperature  is  practically  the 
same  in  the  two  instances.  One's  feeling  of  warmth  is  in 
the  skin;  if  the  blood  vessels  in  the  skin  are  open  so  that 
much  warm  blood  can  flow  through  them,  one  feels  warm; 


THE  SKIN  239 

if  they  are  partly  closed  so  that  the  blood  is  kept  inside 
[the  body,  one  feels  cold. 

The  larger  part  of  the  heat  of  the  body  is  produced  in  the 

[muscles  when  they  contract,  though  a  great  deal  seems  to 

)e  formed  in  certain  glands  like  the  liver.     This  heat  warms 

ihe  blood   flowing  through   these   organs.     Then   the   blood 

;oes  to  the  cooler  parts  of  the  body,  warming  them  in  much 

the  same  way  as  hot  water  warms  the  different  rooms  of  a 

house,  as  it  goes  to  them  through  pipes  from  a  heater.     The 

blood  thus  distributes,  but  does  not  produce  heat. 

Cold  and  Warm-Blooded  Animals. — The  cold-blooded  an- 
imals— frogs,  alligators,  lizards  etc. — are  never  much  warmer 
than  the  air  in  which  they  live.  While  oxidation  of  course 
takes  place  in  them  as  in  other  animals,  and  heat  is  thus 
produced,  there  seems  to  be  no  special  regulation  of  body 
heat,  and  they  have  a  very  low  temperature  on  a  cold  day 
and  a  high  temperature  on  a  hot  day  when  lying  in  the  sun. 
They  are  apt  to  be  sluggish  at  any  time,  but  are  sure  to  be  so  in 
cold  weather. 

In  warm-blooded  animals,  i.  e.  birds  and  mammals,  the 
amount  of  heat  produced  is  always  great,  and  the  temperature 
of  the  body  does  not  change  with  the  temperature  of  the  air 
but  remains  constant  if  the  animal  is  in  uniform  health. 
Such  animals  are  called  warm-blooded  because  their  blood  is 
generally  warmer  than  the  air,  although  on  a  hot  summer 
day  it  may  be  cooler  than  the  air.  To  maintain  a  constant, 
high  temperature  a  considerable  amount  of  heat  must  be 
produced  and  consequently  a  large  amount  of  food  must 
be  oxidized.  Warm-blooded  animals  thus  demand  much 
more  food  than  cold-blooded.  A  turtle's  activities  are  so 
slight  that  the  little  energy  stored  in  its  body  is  sufficient  to 
keep  it  alive  for  six  months  without  food  while  a  warm-blooded 
animal  must  have  a  large  supply  of  food,  and  can  live  only 
a  comparatively  short  time  if  deprived  of  it. 

The  Regulation  of  Temperature. — The  temperature  of  the 


240  ADVANCED  PHYSIOLOGY 

body  can  evidently  be  modified  either  (1)  by  changing  the 
amount  of  heat  produced,  through  an  increase  or  decrease  in 
the  amount  of  food  oxidized;  or  (2)  by  varying  the  amount  oj 
heat  lost.  Each  of  these  methods  is  adopted  in  part;  but  under 
ordinary  conditions  it  is  by  controlUng  heat  loss  that  this 
regulation  is  chiefly  effected.  To  appreciate  this  fact  it 
must  be  understood  that  the  heat  resulting  from  the  ordinary 
oxidation  of  food  is  more  than  enough  to  warm  the  body  and 
keep  it  at  98°  F.  To  maintain  the  correct  body  temperature, 
therefore,  it  is  necessary  that  some  heat  be  passed  off. 

Loss  of  Heat  through  the  Lungs. — When  the  temperature 
of  the  air  is  considerably  lower  than  that  of  the  body,  as  is 
usually  the  case,  one  loses  superfluous  heat  in  breathing. 
The  inhaled  air  is  cooler  than  the  body,  but  when  exhaled 
its  temperature  has  been  raised.  Of  course,  if  the  air  has 
thus  been  warmed  the  body  has  been  correspondingly  cooled. 
The  cooler  the  air  breathed  the  more  heat  it  will  take  from 
the  blood.  On  a  cold  day  so  much  heat  may  be  lost  by  this 
means  as  to  take  away  nearly  all  the  surplus;  but  when  the 
air  is  warmer  this  loss  is  not  sufficient  for  the  purpose  of  keep- 
ing the  body  temperature  uniform. 

Loss  of  Heat  from  the  Skin. — The  chief  method  of  regulating 
body  heat  is  by  the  expansion  and  contraction  of  the  blood 
vessels  in  the  skin.  Since  the  air  is  almost  always  cooler 
than  the  blood,  blood  will,  of  course,  be  cooled  as  it  flows 
through  the  skin;  and  the  more  rapidly  the  warm  blood  flows 
through  the  skin,  the  more  rapid  will  be  the  loss  of  heat. 
But  while  this  swift  flow  actually  cools  the  body,  it  seems  to 
make  it  warmer.  This  is  due  to  the  fact  that  the  skin  is 
very  sensitive  to  temperature,  and  when  an  extra  amount  of 
warm  blood  is  flowing  through  it  a  feeling  of  extra  warmth 
will  be  experienced,  though  the  body  is  actually  cooling. 

One  often  feels  this  to  be  true  when  a  sore  finger  is  bandaged 
and  a  string  tightly  tied  about  it;  the  end  of  the  finger  feels  cold 
because  free  movement  of  the  blood  has  been  prevented  by  the 


THE  SKIN  241 

ligature.  A  rubber  band  tightly  wound  on  the  finger  gives 
similar  evidence  of  the  same  fact. 

Expansion  and  Contraction  of  Blood  Vessels  in  the  Skin. — 

We  have  already  noticed  how  readily  the  small  blood  vessels 
are  expanded  and  contracted  by  the  action  of  muscles  in 
them  and  that  this  action  is  controlled  by  nerves.  In  the 
skin  the  muscles  in  the  small  arteries  are  especially  well 
developed  and  quickly  relax  or  contract  under  the  influence  of 
extra  heat  or  cold.  If  the  temperature  of  the  air  rises  on  a 
warm  day,  if  the  body  is  warm,  or  if  extra  heat  is  being  pro- 
duced, the  blood  vessels  in  the  skin  relax.  In  short,  when- 
ever the  heat  being  produced  in  the  body  is  greater  than  that 
required  to  maintain  the  proper  temperature  a  relaxation  of 
the  skin  vessels  allows  more  blood  to  come  to  the  surface, 
thus  increasing  the  loss  of  heat.  Whenever  heat  loss  from 
the  skin  is  greater  than  heat  production,  so  that  the  body  is 
cooling  too  rapidly,  the  skin  vessels  contract  and  allow  less 
blood  to  flow  through  them.  This  keeps  the  warm  blood 
inside,  and,  of  course,  prevents  the  body  from  cooling  too 
rapidly.  The  perfect  control  which  the  brain  thus  has  over 
these  vessels  enables  it  to  regulate  the  amount  of  blood 
flowing  through  the  skin  and,  consequently,  the  amount  of 
heat  lost  through  direct  radiation  from  the  body. 

Perspiration  as  a  Heat  Regulator. — There  is  another  means 
by  which  loss  of  heat  through  the  skin  is  regulated.  The 
sweat  glands  are  constantly  pouring  their  secretion  upon  the 
skin,  where  it  is  as  constantly  evaporated.  It  is  a  simple 
law  of  physics  that  heat  is  required  to  evaporate  moisture. 
Hence  the  larger  the  amount  of  sweat  poured  upon  the  skin 
for  evaporation,  the  greater  will  be  the  amount  of  heat  re- 
quired for  evaporating  it,  and  therefore  any  increase  of  per- 
spiration increases  the  heat  lost  by  this  means.  Everyone 
knows  that  the  amount  of  sweat  increases  with  the  tempera- 
ture. On  a  hot  day  one  perspires  profusely,  and  on  a  cold 
day  imperceptibly.     All  these  sweat  glands  are  supplied  with 


242  ADVANCED  PHYSIOLOGY 

nerves  in  such  a  way  that  the  brain  can  increase  or  decrease 
the  amount  of  their  secretion.  When  the  air  becomes  so  warm 
that  it  is  difficult  for  the  skin  to  lose  by  simple  radiation  an 
amount  of  heat  sufficient  to  keep  the  body  temperature  at 
its  proper  point,  the  sweat  glands  increase  their  action.  In 
the  evaporation  of  the  extra  moisture  thus  poured  out  on  the 
body  surface  so  much  heat  is  lost  that  the  body  temperature 
is  reduced  to  its  proper  level. 

After  a  bath,  even  though  the  water  used  be  warm,  and  the 
room  at  more  than  usual  temperature,  this  same  sense  of  cool- 
ness is  felt.  People  often  say  while  swimming  in  a  river  or  the 
ocean,  ''The  water  is  warm  enough  but  the  air  is  chilly.'* 

The  extent  to  which  body  heat  may  be  reduced  through 
sv/eat  evaporation  is  really  very  great.     One  experimenter 
found  that  he  could  remain  for  some  time  in  a  room  in  which, 
the    air  was  warmer  than  260°  F.  and  in  which  the  direcl 
effect  of  the  air  would  be,  of  course,  to  warm  the  blood  rather' 
than  cool  it.     But  evaporation  of  the  profuse  perspiration^ 
resulting  took  so  much  heat  from  his  body  that  he  found 
perfectly  possible  to  retain  his  normal  temperature.     Stokers] 
on  ocean  steamers,  living  and  working  as  they  do  in  a  tem- 
perature of  over   130°  F.,  are  evidence  that  this    principle 
admits  of  constant  and  daily  application.     The  fact  that 
fever  is  accompanied  by  the  lack  of  perspiration,  partialb 
explains  the  rise  in  the  temperature  of  the  body  at  such] 
times. 

SUMMARY  OF  METHODS  OF  HEAT  REGULATION 

As  an  illustration  of  heat  regulation  in  the  body,  imagine] 
a  hot  summer  day  with  the  temperature  of  the  air  over  100°  F. 
The  air  is  actually  warmer  than  the  body;  the  sweat  glands] 
pour  out  an  abundant  secretion  which  rapidly  evaporates. 
This  evaporation  cools  the  skin  and  reduces  the  temperature  ofj 
the  body  to  the  desired  point. 


THE  SKIJM  243 


Hfeuppose  the  temperature  of  the  air  falls  to  85°  F.     Profuse 
I  sweating  ceases;  perspiration  does  not  stop,  but  the  sweat  is 
1  less  abundant,  does   not  collect  so  profusely  in  drops,  and  a 
!  different  method  of  controlling  body  heat  comes  into  play.  The 
blood  is  now  warmer  than  the  air,  and  will  be  cooled  as  it 
flows  through  the  skin;  owing  to  the  heat,  the  skin  vessels  re- 
main relaxed  and  large  amounts  of  blood  from  the  internal 
organs  are  coming  to  the  surface.     The  skin  is  thus  filled 
with  warm  blood  and  the  person  still  feels  warm,  though 
the  blood  is  being  cooled  by  the  air.     Heat  thus  passes  off 
I  by  direct  radiation  in  sufficient  quantities  to  keep  body  tem- 
I  perature  at  the  proper  point. 

Suppose  now  that  the  temperature  falls  to  about  70°  F. 
Sensible  perspiration  stops  entirely;  the  blood  vessels  of  the 
!  skin  partly  close  so  that  less  warm  blood  flows  through  them; 
the  body  retains  its  heat  in  this  way,  and  its  general  tem- 
perature remains  the  same  as  before.  If  the  external  tempera- 
ture falls  still  more,  a  different  adjustment  is  necessary.  The 
skin  vessels  constrict  still  further,  and  the  warm  blood  is 
confined  to  the  internal  organs  until  they  are  almost  over- 
supplied  with  blood.  Now  since  so  little  blood  is  flowing 
through  the  skin,  the  person  begins  for  the  first  time  to  feel 
chilly,  and  it  is  at  this  temperature,  i.e.  between  70°  and  60°  F., 
that  one  is  most  liable  to  take  cold.  If  the  temperature  falls 
yet  lower,  more  heat  must  be  produced  by  increased  oxida- 
tion. Thus  at  temperatures  above  70°  F.  regulation  of  body 
heat  is  brought  about  by  increasing  or  decreasing  the  loss  of 
1  heat;  below  this,  chiefly  by  increasing  heat  production. 

It  is  important  to  realize  the  significance  of  a  constant 
body  temperature;  man  can  exist  only  while  warmth  is  as- 
sured and  if  its  supply  were  not  regulated,  he  could  live  only 
in  certain  climates.  Because  of  this  automatic  control  of 
body  temperature  man  can  live  in  summer  or  winter,  in  the 
cold  regions  of  the  north,  or  in  the  hot  climate  of  the  equator. 
Animals  with  an  abundance  of  hair  do  not  perspire  pro* 


244  ADVANCED  PHYSIOLOGY 

fusely,  and  their  skin  has  Httle  power  of  regulating  tempera- 
ture. Such  animals  must  depend  largely  upon  respiration 
to  rid  themselves  of  surplus  heat.  This  explains  the  panting 
of  dogs,  and  their  rapid  breathing  in  hot  weather  or  when 
exercising   rapidly. 

CARE  OF  THE  SKIN 

To  insure  the  healthful  functioning  of  the  skin,  the  pores 
of  the  sweat  glands  must  be  kept  free  and  open.  The  fat 
glands  connected  with  the  hair  follicles  are  constantly  exuding 
a  certain  amount  of  oil,  and  the  sweat  glands  give  out  much 
water,  salts  and  other  substances.  The  water  will  readily 
evaporate,  but  the  solid  material  will  remain  on  the  skin, 
tend  to  clog  the  pores,  check  the  ready  action  of  the  glands 
and  cause  an  offensive  odor.  Evidently  the  normal  action 
of  the  skin  demands  that  this  material  be  removed.  To  keep 
the  pores  open,  habitual  bathing  and  washing  of  the  skin  is 
a  necessity.  The  frequency  of  the  bath,  however,  is  a  matter 
in  regard  to  which  no  rule  can  be  given.  A  daily  bath  is 
certainly  desirable,  though  doubtless  not  necessary  to  health. 

It  is  a  mistake  to  suppose  that  cleanliness  is  the  primary 
benefit  to  be  derived  from  bathing,  although  it  is  an  im- 
portant one.  The  principal  effect  of  the  bath  is  in  stimu-  ; 
lating  the  skin,  and  increasing  its  activity.  The  skin  is  a  it 
delicate  organ,  in  which  more  blood  is  exposed  to  the  air  than  » 
in  any  other  organ  in  the  body.  A  large  part  of  one's  com-  t 
munications  with  the  outer  world  are  received  through  it.  I 

Cold  Baths. — The  first  effect  of  a  cold  bath,  whether  it  be  a 
plunge  in  cold  water,  a  shower  bath  or  merely  a  sponge  bath, 
is  to  stimulate  the  temperature  nerves  of  the  skin,  producing  n 
decided  sensation  of  cold.  This  acts  through  the  brain  and 
causes  (1)  a  contraction  of  the  blood  vessels  in  the  skin;  for 
a  short  time  the  skin  becomes  white  and  cold,  due  to  this 
contraction.  But  this  is  presently  followed  by  (2)  a  reaction; 
almost  immediately  the  brain  withdraws  its  contracting  in- 


I 


THE  SKIN  245 


fluence  allowing  the  vessels  to  expand.  More  blood  now 
flows  through  the  skin,  it  becomes  flushed  and  warm,  and 
there  is  a  feeling  of  exhilaration  in  the  body.  This  ''  after- 
glow "  may  last  a  long  time,  and  the  person  should  leave  the 
water  while  still  under  its  influence.  If  he  stays  in  longer, 
the  blood  vessels  may  again  contract,  making  him  chilly, 
and  since  this  time  there  is  no  subsequent  reaction  to  warm 
the  body,  he  is  Ukely  to  be  cold  and  uncomfortable  for  many 
hours.  The  length  of  time  that  the  after-glow  may  continue 
depends  upon  the  person,  the  temperature  of  the  water  and 
to  a  certain  extent  upon  its  character,  lasting  longer  if  the 
water  is  salt,  than  if  fresh. 

The  after-glow  from  a  cold  bath  is  increased  if  it  is  accom- 
panied by  a  vigorous  friction  of  the  skin.  Energetic  rubbing 
with  a  rough  towel  is  of  as  much  value  as  the  bath  as  a  stimu- 
lant for  the  skin,  and  without  it  the  bath  accomplishes  only 
half  its  purpose.  Rubbing  with  towels  pulls  to  a  slight  degree 
on  every  part  of  the  surface,  stretches  the  different  tissues  in 
the  dermis,  dislodges  any  loose  epidermis,  and  leaves  the  skin 
alert  and  ready  to  perform  its  duties.  In  short,  the  cold 
bath  and  the  ''  rub  "  are  to  the  skin  what  the  gymnasium  is 
to  the  skeletal  muscles. 

Since  one  of  the  chief  objects  of  the  cold  bath  is  to  shock 
the  skin,  there  is  no  reason  why  one  should  not  take  a  plunge 
into  cold  water,  even  when  hot  and  sweaty,  provided  he 
does  not  stay  in  long  enough  to  become  chilled.  The  shock 
is  an  advantage,  the  cooling  is  refreshing.  On  the  other  hand 
to  take  a  cold  plunge  when  one  is  already  cold  is  neither 
pleasant  nor  profitable,  unless  it  is  followed  at  once  by  a 
vigorous  friction  which  develops  the  proper  aft6r-glow.  Cold 
baths  should  always  be  taken  when  one  is  warm,  e.g.  when 
just  out  of  bed  or  after  vigorous  exercise.  After  a  night's 
rest  in  a  horizontal  position,  the  heart  is  beating  slowly,  blood 
is  flowing  sluggishly  and  nerves  are  stupid.  A  cold  bath  at 
such  a  time  is  the  best  stimulant  a  person  can  take  to  get 


246  ADVANCED  PHYSIOLOGY 

himself  thoroughly  awake,  arouse  his  nerve  centers  and  start 
the  human  machine  going  for  the  day. 

Hot  Baths. — There  are  times  when  hot  baths  are  desirable. 
Warmth  is  sure  to  produce  an  expansion  of  the  blood  vessels 
of  the  skin,  and  thus  to  a  certain  extent  draw  blood  from  the 
internal  organs.  This  may  be  very  beneficial;  for  example, 
it  may  enable  one  to  get  to  sleep,  or  rest  when  restless,  since 
it  draws  blood  from  the  brain.  When  one  has  the  first  symp- 
toms of  a  cold,  a  hot  bath,  or  even  heating  the  feet  in  hot 
water,  may  withdraw  the  blood  from  the  inflamed  throat  or 
nasal  cavities  and  check  the  onset  of  the  cold.  This  method 
v^f  causing  the  expansion  of  the  vessels  is  not  so  good  an 
exercise  for  the  skin  as  the  cold  bath,  and  is  not  really  an  in- 
vigorating stimulant;  it  tends  to  leave  the  skin  soft  and  deli- 
cate, and  the  body  should  be  warmly  covered  after  such  a 
bath,  and  not  exposed  to  any  chill.  Hot  baths  should  never 
be  taken  immediately  after  meals,  for  the  blood  rushing  to 
the  skin  to  fill  the  relaxed  capillaries  is  taken  from  the  diges- 
tive organs  which  then  need  it.  Skin  activity  is  the  best 
guard  against  the  various  skin  diseases.  A  skin  kept  healthy 
by  bathing  and  friction  will  ward  off  many  an  attack  of  para- 
sitic bacteria  to  which  an  unhealthful  skin  would  yield. 

CLOTHING 

Much  contradictory  advice  is  given  concerning  the  kind  and 
amount  of  clothing  it  is  best  to  wear.  Fortunately  the  body 
so  easily  adapts  itself  to  conditions  that  it  can  get  along  with 
many  differences  in  method  of  treatment. .  While  specific 
rules  for  clothing  cannot  be  given,  certain  principles  are 
involved. 

Clothing  serves  two  purposes:  (1)  to  conserve  warmth,  and 
(2)  to  absorb  the  perspiration  of  the  body.  The  amount  of 
warmth  that  any  fabric  seems  to  give  is  dependent  not  only 
on  its  thickness,  or  weight,  but  also  upon  the  size  and  num- 
ber of  air  spaces  in  the  cloth.     Air  is  a  very  poor  conductor 


|H|  THE  SKIJNT  247 

V^Mf  heat  and  cold.  Coarse  cloth  in  the  meshes  of  which  are 
^^Bumerous  air  spaces  is,  therefore,  warmer  than  closely  woven 
^^Rloth  of  equal  weight.  For  the  same  reason,  two  or  more 
i  thicknesses  of  cloth  are  warmer  than  one  of  equal  weight, 
I      the  air  space  between  the  two  holding  the  heat. 

If  we  were  to  live  out  of  doors  in  the  winter,  much  heavier 
clothing  would  be  needed  than  in  warm  weather;  but  most  of 
us  spend  the  greater  part  of  our  time  in  rooms  whose  tempera- 
ture is  very  little  colder  than  that  of  summer  and  although  we 
do  go  out  into  the  cold,  a  comparatively  small  amount  of 
our  time  is  thus  spent.  For  most  people,  therefore,  it  is  plainly 
a  mistake  to  dress  the  body  warmly  all  the  time  because  of 
the  occasional  minutes  spent  outside.  The  wiser  method  is 
to  wear  the  same  amount  of  clothing  that  one  would  wear  at 
those  seasons  when  the  outside  temperature  is  about  the 
same  as  that  maintained  in  one's  living  rooms  in  the  winter, 
and  then  to  add  upon  going  out  of  doors  such  clothing  as  is 
necessary  for  comfort.  If  one  lives  out  of  doors  much  of 
the  time  in  winter  the  case  is  different.  The  amount  of  cloth- 
ing needed  for  very  cold  weather  varies  much  with  different 
people,  depending  largely  upon  whether  one  has  invigorated 
his  skin  or  has  allowed  it  to  become  sluggish.  One  should 
remember  that  the  primary  reason  he  wears  heavy  clothing 
in  winter  is  for  comfort  and  not  to  prevent  taking  cold. 
Indeed,  an  increase  in  exercise  is  a  far  more  efficient  means 
of  meeting  an  ordinary  winter's  cold  than  is  the  practice  of 
bundling  the  body  heavily  with  wraps.  Most  people  make 
the  mistake  of  wearing  too  much  clothing  in  winter,  thus 
reducing  their  powers  of  resistance. 

The  clothing  worn  next  the  skin  should  be  of  a  character  to 
absorb  the  water  of  perspiration  readily.  Cotton  cloth  is  an 
excellent  absorbent  and  gives  the  water  off  again  readily. 
Woollen,  which  does  not  absorb  water  so  readily  and  is  apt  to 
hold  it  without  allowing  sufficient  evaporation,  should  not  be 
worn  next  the  skin  at  times  when  perspiration  is  abundant. 


248  ADVANCED  PHYSIOLOGY 

In  summer  weather  underclothing  should  be  of  cotton  or  of 
tsome  good  absorbent  material  rather  than  of  wool.  In  winter 
when  the  amount  of  perspiration  is  less  and  its  evaporation 
from  the  skin  a  matter  of  much  smaller  consequence  than  in 
summer,  woollen  underclothing  is  not  unwise,  although  cotton 
is  entirely  suitable.  If  one  passes  most  of  his  time  in  winter 
in  highly  heated  rooms,  he  should  wear  the  same  kind  of 
underclothing  that  he  wears  in  the  spring  and  fall. 

BURNS  AND  FROSTBITES 

Although  burns  and  frostbites  are  extremely  common  in- 
juries to  the  skin,  either  of  them  may  be  serious  if  severe. 
Ordinary  burns  may  be  simply  treated.  After  the  pain  has 
been  relieved  by  plunging  the  burned  part  into  cold  water  or 
bathing  it  with  water  containing  common  baking  soda,  the 
application  of  a  little  vaseline  to  exclude  the  air  is  all  that  is 
necessary. 

If  the  clothing  catches  fire,  however,  prompt  action  and 
more  careful  treatment  are  required.  Pick  up  anything  at 
hand  which  will  serve  as  a  wrapper;  a  rug,  blanket,  shawl, 
or  overcoat  will  serve.  Wrap  the  person  quickly  to 
smother  the  flames,  throwing  him  down  if  necessary  and 
rolling  him  over  and  over  in  the  wrapping  material.  After 
the  flames  are  extinguished  remove  the  clothing  from  the 
burned  spots  with  great  care  and  gentleness,  cutting  it  and 
softening  it  with  water  if  it  adheres  to  the  skin.  Be  especially 
careful  not  to  break  the  blisters  that  have  formed.  Then 
anoint  the  burned  parts  with  vaseline,  and  in  all  severe  cases 
summon  a  physician  at  once. 

Frostbites  are  generally  confined  to  the  fingers  and  toes, 
ears  and  nose;  in  other  words,  to  those  parts  where  the  blood 
flow  is  least  vigorous  and  where  there  is  a  large  surface  ex- 
posed to  the  cold  air.  The  muscles  may,  however,  be  con- 
cerned as  well  as  the  skin.  When  a  limb  is  frozen  the  water 
in  the  blood  and  muscles  is  partly  turned  into  ice.     If  it  is 


THE  SKIN  249 


I  thawed  slowly,  the  water  may  resume  its  former  relations 
and  the  body  activities  continue  as  before.  But  if  thawed 
out  rapidly,  the  water  will  not  return  to  its  normal  condition, 
and  inflammation,  together  with  the  final  destruction  of  the 
frozen  part,  may  follow.  For  this  reason  the  treatment  of 
frostbites  or  frozen  parts,  should  be  such  as  to  cause  them 
to  thaw  slowly.  Rubbing  frozen  parts  with  snow  or  cold 
water  is  usually  recommended,  for  this  will  slowly  thaw  them 
with  the  least  danger  of  injury.  The  preservation  of  the 
frozen  member  depends  largely  upon  prompt  action  although 
the  thawing  must  be  very  gradual.  The  person  should  be 
warmly  wrapped  and  after  normal  activities  have  been  resumed, 
some  sort  of  hot  drink  should  be  administered. 

Smallpox,  Scarlet  Fever,  Measles. — These  three  diseases, 
although  distinct,  are  all  characterized  by  skin  eruptions. 
They  are  all  contagious  and  all  occur  as  epidemics,  many  cases 
appearing  in  a  community  at  once.  The  ease  with  which  one 
person  takes  them  from  another  makes  it  necessary  to  isolate 
the  patients  and  to  quarantine  the  house  they  occupy.  The 
cause  of  none  of  these  diseases  is  positively  known,  although 
they  are  doubtless  due  to  germs  of  some  sort.  The  only  methods 
of  preventing  them  are  by  avoiding  association  with  patients, 
and,  in  the  case  of  small-pox,  by  vaccination. 

Smallpox  is  the  most  serious  of  the  three  and,  formerly  pro- 
duced frightful  ravages.  To-day  it  is  largely  controlled  by 
vaccination.  It  is  probably  distributed  by  particles  discharged 
through  the  skin.  It  is  to  be  avoided  by  keeping  away  from 
persons  with  the  disease,  and  by  vaccination  (page  386). 

Scarlet  fever  and  measles  are  also  serious.  The  infectious 
material  is  certainly  contained  in  the  sputum  and  the  dis- 
charges from  the  nose  of  the  patient  and  perhaps  in  the  particles 
given  off  from  his  skin.  To  avoid  these  diseases  we  must  shun 
those  sick  with  them,  and  remember  that  the  infectious  material 
is  dangerous  whether  moist  or  dry,  and  that  it  may  be  carriQcJ 
upon  toys  or  clothing. 


CHAPTER  XVI 
THE  SKELETON 

We  have  seen  how  foods  furnish  the  body  with  heat  and 
act  as  a  source  of  human  energy  in  general;  we  may  now  give 
attention  to  the  more  permanent  forms  which  foods  take  as 
body  tissues,  studying  especially  the  skeleton  and  the  mus- 
cles, which  form  the  largest  part  of  the  body  in  bulk. 

The  Functions  of  the  Skeleton. — The  function  of  the  skele- 
ton is  two-fold. 

1.  It  gives  firmness  to  the  body;  without  such  a  frame* 
work,  the  other,  softer  tissues  would  form  but  a  shapeless 
mass,  with  no  means  of  bracing  itself  for  doing  work. 

2.  It  furnishes  attachments  for  muscles,  and  thus  makes 
motions  possible;  muscles  are  so  fastened  to  the  bones  as  to 
move  them,  thus  producing  movements  of  the  body. 

All  large  animals,  except  a  few  living  in  the  ocean  (jelly- 
fishes,  etc.),  have  skeletons  of  one  sort  or  another;  it  is  the 
only  method  nature  has  devised  for  holding  together  large 
masses  of  soft  tissues  and  making  it  possible  for  them  to 
work  to  purposive  ends.  In  some  animals,  e.  g.  lobsters,  in- 
sects, clams,  etc.,  the  skeleton  is  a  mere  crust  on  the  outside, 
and  thus  is  called  an  exoskeleton ;  but  the  circumstances  are  the 
reverse  with  all  ''backboned"  animals,  including  man,  which 
are  spoken  of  as  possessing  an  endoskeleton.  In  the  adult 
human,  the  skeleton  makes  up  about  16%  of  the  weight  of  the 
entire  body,  and  comprises  about  two  hundred  separate  bones; 
the  child's  skeleton  contains  more  because  during  the  process 
of  growth  some  bones  fuse  together.  In  spite  of  their  number, 
the  bones  are  so  strongly  bound  together  by  tough,  stringy 
haments  and  by  muscles  that  the  whole  skeleton  forms  a  very 

fiirm,  solid  unit;  Fig.  120. 

250 


THE  SKELETON 


251 


For  convenience  in  study,  the 
skeleton  may  be  considered  as 
consisting  of  two  parts.  (1)  The 
axial  skeleton,  made  up  of  the 
backbone,  ribs  and  skull,  forming 
the  main  axis  of  the  body  and 
the  most  rigid  part  of  the  whole; 
(2)  the  appendicular  skeleton, 
or  skeleton  of  the  appendages 
(arms  and  legs).  In  most 
animals,  e.g.  dogs,  cats  and 
horses,  both  arms  and  legs  are 
organs  of  locomotion;  in  birds 
the  front  appendages  are  modified 
as  wings,  while  in  man  they  are 
not  organs  of  motion,  but  grasp- 
ing organs  (organs  of  prehension). 
In  man  alone  the  arm  and  hand 
are  used  for  this  purpose  only 
though  some  of  the  monkeys  use 
them  for  prehension  as  well  as 
for  locomotion. 

AXIAL  SKELETON 

Spinal    Column. — The    central 
part    of   the    axial    skeleton    is 
called   the   backbone,    or   spinal 
column.     This   is   not   a    single 
bone  but  a  series  of  vertebrae,  ir- 
regular bones  placed  one  on  top 
of  the  other  and  firmly  bound  to- 
gether; Fig.  121.    Seven  ring-like 
vertebrae  in  the  neck  are  called  the 
cervical    vertebrae;  twelve  below 
these   are    nearly   alike  and  are 


Fig.    120 — Human  skeleton 

A,  Frontal;  B,  Clavicle;  C, 
Sternum;  D,  Scapula;  E,  Hu- 
merus; F,  Radius;  G,  Ulna;  H 
Carpals;  /,  Metacarpals;  J, 
Phalanges;  K,  Vertebrae;  L, 
Pelvis;  M,  Femur;  N,  Patella; 
O,  Fibula;  P,  Tibia;  Q,  Tarsals; 
R,  Metatarsals;  S,  Phalanges. 


252 


ADVANCED  PHYSIOLOGY 


)Cervicai 


)  Dorsal 


termed  the  dorsal  vertebrae;  five  heavier  ones  in  the  "small'* 
of  the  back  are  the  lumbar  vertebrae. 

Although  the  vertebrae  differ  in  shape  and  size,  each  con- 
sists of  a  rounded  portion  with  flat 
upper  and  lower  surfaces,  the  centrum, 
on  the  sides  of  which  arise  two  pieces 
of  bone  uniting  to  form  the  neural  arch ; 
where  these  two  projections  are  joined, 
they  are  prolonged  into  a  spine,  the 
neural  process;  Figs.  122  and  123. 
When  the  vertebrae  are  placed  on  top 
of  each  other,  with  the  spines  pointing 
backward,  the  arches  are  brought  over 
each  other  and  the  openings  in  the 
successive  vertebrae,  i.e.  the  neural 
foramina,  together  form  a  long  tube 
just  in  front  of  the  row  of  spines.  This 
tube,  completely  surrounded  by  bone, 
contains  the  spinal  cord,  an  organ  of 
great  importance  and  delicacy,  which 
is  thus  protected  from  all  ordinary 
injuries.  When  in  position  in  the  back 
they  do  not  actually  touch  one  an- 
other, for  between  each  two  is  an 
elastic  pad  of  cartilage  which  serves 
as  a  cushion  to  relieve  jars.  The 
vertebrae  are  connected  by  ligaments, 
running  between  every  two  vertebrae 
and  thus  tightly  binding  all  the  parts 
of  the  spinal  column  into  a  firm  support. 
Although  the  backbone  is  as  a  result  a 
strong  structure,  it  possesses,  never- 
theless, a  certain  amount  of  flexibility.  It  has  the  greatest 
amount  of  strength  consistent  with  easy  bending  of  the  body 
from  side  to  side,  or  forwards   and  backwards.     The  verte- 


^acral 


(Coccyx 
121. — The  spinal 

COLUMN 
Showing    the    curves    and 
the     separate       vertebrae 
(Thompson). 


THE    SKELETON 


253 


'Dj  for  Btood  vessel 


Centrum 


Fig.  122. — One  of  the  dorsal  verta 
br^  viewed  from  the  side 


brae  are  so  united  as  to  form  a  column  of  bones  with  graceful 
curves  (Fig.  121),  an  arrangement  which  in  itself  has  more  of 
the  qualities  of  a  spring 
than  are  possessed  by  a 
straight  column. 

In  order  that  the  legs 
may  firmly  support  the 
heavy  body,  strong  con- 
nection of  the  "hipbones" 
to  the  spine  is  necessary. 
To  make  this  junction 
solid,  five  of  the  vertebrse 
in  that  region  are  enlarged 
and  grown  together,  form- 
ing the  sacrum;  Figs.  121 
and  124.  Below  this  are 
four  much  smaller  ver- 
tebrse, partially  grown 
together  and  called  the 
coccyx.  It  is  the  con- 
tinuation of  this  which 
forms  the  '  tail  in  some 
animals. 

The  Ribs  and  Sternum. 
— The  ribs  are  a  series 
of  slender  arching  bones, 
attached  at  one  end  to 
the  twelve  dorsal  verte- 
brse, and  bending  outward 
and  forward  to  enclose 
the  thorax  or  chest  cav- 
ity. The  lower  ribs  afford 
some  protection  to  the 
upper  part  of  the  abdo- 
men  also.      After    arching   around   the    chest   the   ribs    are 


Neural  Process 


Centrum 


Fig.  123. — One  op  the  dorsal  verte- 
bra   VIEWED  FROM  ABOVE 


254 


ADVANCED    PHYSIOLOGY 


Fig.  124. — The  sacrum 

Consisting  of  five  fused  vertebrae  at  the 
lower  end  of  the  spinal  column. 


connected   indirectly   with  the  sternum  by  short  pieces  of 
cartilage;  Fig.  101.     This  material  is  more  flexible  and  elastic 

than  bone,  thus  making  it 
possible  for  the  ribs  to  move 
freely  without  danger  of 
breaking.  Two  of  the  lower 
ribs  on  each  side,  called  float- 
ing ribs,  are  very  short  and 
are  not  attached  to  the 
sternum  at  all.  The  thorax, 
which  contains  the  heart  and 
lungs,  is  thus  protected  on 
all  sides  by  a  framework  of 
bones. 

The  sternum,  or  "  breast 
bone  "  (Fig.  120),  is  composed 
of  three  flat,  elongate  bones,  placed  end  to  end;  the  uppermost 
is  roughly  shield-shaped,  the  middle  bone  elongate  rectangu- 
lar, and  the  lower  one  triangular,  with  the  point  downward. 
They  are  so  closely  joined  that  little  movement  occurs  be- 
tween them,  and  the  three  are  generally  spoken  of  as  though 
a  single  piece. 

The  Skull. — The  skull  is  balanced  on  the  spinal  column  and 
is  attached  to  the  top  vertebra  in  such  a  way  that  it  may  be 
nodded  backward  and  forward.  The  joint  involved  in 
turning  the  head  from  side  to  side  is  that  between  the  first 
and  second  vertebrae.  The  skull  is  a  complicated  arrangement 
of  bones,  twenty-two  in  all  (Fig.  125),  so  rigidly  fitted 
together  that  there  is  no  motion  between  them,  except  that 
of  the  jaw  bone.  Teeth  are  not  a  part  of  the  skeleton,  since 
they  arise  from  the  lining  of  the  mouth  and  because  this  lining 
is  essentially  the  same  as  the  outer  skin. 

We  may  consider  the  skull  as  made  up  of  three  parts. 

1.    The  cranium,    a  large,  rounded  box  of  bones  firmly 


THE    SKELETON 


255 


united  (Figs.  120  and  125)  and  enclosing  a  large  cavity,  is  filled 
by  the  brain,  the  center  of  all  mental  activity.  The  cranium 
is  made  of  eight  large  bones,  which  in  the  adult  are  dove- 
tailed together,  the  lines  where  they  meet  being  called  su- 
tures. In  childhood, 
while  the  skull  is  grow- 
ing, they  are  soft  and 
not  so  firmly  joined, 
though  they  touch  each 
other.  If  a  young 
baby's  head  be  ex- 
amined, there  will  be 
found  a  soft  spot  in 
the  middle  where  the 
bones  have  not  yet 
come  together;  Fig. 
126. 

2.  The  facial  bones, 
thirteen  in  number, 
form  the  face.  They 
enclose  the  eyes  and 
comprise  the  cheek 
bones  and  upper  jaw. 

3.  The  mandible, 
forming  the  lower  jaw, 
is  a  single  bone  hinged  to  the  temporal  bone  of  the  cranium, 
Fig.  125.  The  only  movable  bone  in  the  skull,  it  is  acted 
on  by  powerful  muscles  attached  to  each  side  of  the  cranium 
and  is  provided  with  a  blade-like  extension  of  its  surface,  so 
that  there  may  be  a  larger  area  for  the  attachment  of  the 
muscle. 

It  will  be  noticed  that  the  skull  is  especially  adapted  to 
the  protection  of  several  delicate  organs  of  the  nervous  system. 
The  brain  itself  is  entirely  inclosed  in  bones  which  are  so 
thick  that  ordinary  blows  can  not  injure  it.     The  eyes  are 


Fig.  125. — The  skull  disarticulated 

,e.    with    the    bones    slightly    pulled    apart    but 
retaining  their  relative  positions. 


256 


ADVANCED    PHYSIOLOGY 


Fig.    126.— Top     of     a 
baby's  skull 

Showing  the  bones  of  the 
cranium  not  yet  grown 
together.  Upper  side  of 
figure  is  posterior. 


sunken  in  deep  bony  pits,  formed  by  the  bones  in  the  eye- 
brows, nose  and  cheek  which  thus  ensures  them  against  injuries. 

The  ears  are  best  protected  of  all, 
since  the  real  hearing  parts  are 
completely  inclosed  in  hard  bone 
inside  the  skull,  only  narrow  pass- 
ages connecting  them  with  the 
exterior. 

THE  APPENDICULAR  SKELETON 

The  Shoulder  and  the  Arm. — Each 
shoulder,  or  pectoral  girdle,  is  made 
of    two  bones.       (1)   The    shoulder 
blade  is  an  oddly  shaped,  triangular 
bone  on  the    back  of  the  shoulder 
joint.     To  this  scapula,  the   upper 
bone  of   the    arm   is    hinged    (Fig. 
127)  and  a  shallow  cavity 
in  it  forms  a  part  of  the 
shoulder  joint.     (2)  The 
collar  bone   or  clavicle, 
which  is  slender  and  in 
such  a  position  as  to  be 
easily   broken,    extends 
from  the  sternum  to  the 
shoulder  joint,  thus  brac- 
ing  the    scapula;     Fig. 
120. 

The  first  bone  in  the 
arm  is  called  the  humer- 
us and  extends  from  the 
shoulder  to  the  elbov/, 
Fig.  128.  Between  the 
elbow  and  wrist  are  two  bones,  the  radius  and  ulna,  the 
former  on  the  same  side  as    the    thumb.     The   ulna   alone 


Seopula 


Big.   127. 


-The  bones  that    form   the 

SHOULDER    joint 


THE    SKELETON 


257 


Carpals 


Meiacan 


enters  the  elbow  joint  with  the  humerus  and  is  large  at  that 
end.  The  radius,  which  merely  touches  a 
projection  on  the  humerus,  is  large  at  the 
other  end  and  alone  makes  the  real  joint  with 
the  small  bones  of  the  wrist,  the  ulna  articulat- 
ing with  but  one  of  these. 

In  the  wrist  are  eight  very  small  bones,  the 
carpals,  between  which  very  little  movement 
occurs.     Following  these  is    a    series  of    five 

Humerus  iti  elongate  bones,  the  metacarpals,  which  form  the 

framework  of  the 
body  of  the  hand. 
In  Figure  129  these 
are  seen  jointed  to 
the  wrist  bones;  also 
the  phalanges,  the 
bones  of  the  fingers, 
two  in  the  thumb 
and  three  in  each 
finger. 

The  Hip  and  the 
Leg. — On  first  ex- 
amination, the 
skeleton  of  the  hip 
or  pelvic  girdle 
looks  very  unlike 
that  of  the  shoulder 
girdle;     Fig.      130. 

One  very  large  and  irregular  bone  is  on  each 
side;  it  is  broad  behind  wnere  it  joins  the 
sacral  portion  of  the  backbone;  and  at  the 
point  farthest  from  the  midline,  where  the 
body  protrudes  at  the  hip,  it  presents  a  cavity 
into  which  fits  the  end  of  the  upper  bone  of 

the  leg.     It  curves  around  to  the  front  and  meets  the  bone 


Radius  Wl 


Uino 


Fig.  128.— The 
bones of the 

ARM 

The  radius  and 
ulna  are  shown 
in  the  position 
they  assume 
when  the  hand 
is  held  with  the 
palm  down- 
wards (in  pro- 
nation). 


FhalaiKjes 


Fig.  129. — ^The  bones  of 
the  wrist  and  hand 


258 


ADVANCED    PHYSIOLOGY 


■femur 


Ilium 


corresponding  to  it  on  the  other  side  of  the  body    at  the 
midline.     These  bones,  each  called  the  os  innominatum,  are 
each    made    up   of  three   bones   which  though   separate  in 
childhood  are  fused  into  one  in  the  adult.    Since 
the  scapula  in  the  young  child  also  consists  of 
two  bones  (grown  together  in  the   adult),  the 
two  girdles  were  originally  made  up  of  the  same 
number  of  parts. 

In  the  leg  proper,  one  long  bone,  the  thigh 
bone  or  femur,  extends  from  the  pelvis  to  the 
knee:    Fig.    131.      Between   the   knee  and  the 

ankle  are  two  bones, 
the  tibia  and  fibula. 
The  tibia  is  large  at 
each  end  and  enters 
into  the  knee  and 
ankle  j  oints ;  but  the 
fibula,  which  is 
smaller  and  on  the 
outside,  has  no  con- 
nection with  the 
knee  joint  and  little 
to  do  with  the  ankle. 
Indeed  though 
present  in  the  hu- 
man  body,  the 
fibula  is  entirely  lacking  in  some  of  the  higher 
animals. 

The  ankle  is  supported  by  seven  small  tarsal 
bones;  Fig.  132.  In  early  childhood  there  are 
eight  of  these  as  there  are  of  the  wrist  carpals. 
A  series  of  five  elongated  bones,  the  metatarsals, 
are  joined  to  the  tarsals  and  form  the  skeleton 
of  the  body  of  the  foot.  The  bones  of  the  toes  are  of  the  same 
number  as  those  of  the  fingers  and  are  also  called  phalanges. 


ifi/  for 
Femur 
Pubis 


Fig.  130. — The  hip,  or  pelvic 

GIRDLE 
(The  innominate  bone)  showing  it 
to    be    composed  of    three     fixed 
bones. 


fibula' 


Tibic 


Fig.  131.— 
The  bones 
OF  the  leg 

From  the  thigh 
to  ankle 


THE  SKELETON 


259 


Torsaldoaep 


STRUCTURE  OF  BONE 

Shape  and  General  Structure. — The  shape  of  bones  is  de- 
signed to  render  them  as  strong  and  yet  as  light  as  possible. 
Upon  the  long  bones  of  the  arms  and  legs  comes  the  heaviest 
strain,  and  consequently  they  are  the  ones  most  frequently 
broken.  Every  bone  is  covered  on  the  exterior  with  a  thin 
connective  tissue  membrane  called 
the  periosteum.  This  is  full  of 
blood  vessels  and  by  means  of  the 
material  thus  brought  to  the  bone, 
new  matter  is  added  to  it  so  that 
this  membrane  plays  a  very  impor- 
tant part  in  the  growth  of  the 
skeleton. 

If  a  bone  is  cut  open  lengthwise, 
it  will  be  seen  to  be  hollow  through- 
out most  of  its  length,  while  the 
bone  itself,  especially  in  the  middle 
of  the  shaft,  is  very  hard  and 
tough.  This  arrangement  in  a 
hollow  cylinder  is  known  to  give  the 
greatest  amount  of  strength  possible 
with  the  amount  of  material  used. 
The  ends  of  the  bone  which  are  not 
hollow  are  very  much  larger  than 
the  shaft,  in  order  to  furnish  suffi- 
cient surface  for  the  joint  and  also  for  the  muscles,  which 
are  attached  to  the  bone  near  the  end.  The  larger  the  surface 
the  more  chance  for  the  attachment  of  muscles  and  the 
stronger  their  action.  If  a  bone  at  its  enlarged  ends  were  of 
the  same  dense  structure  as  in  the  middle  of  the  shaft,  the 
whole  would  be  very  heavy;  to  avoid  this  without  materially 
weakening  it,  the  ends  are  spongy  and  porous. 

Marrow. — The  cavities  in  the  middle  of  the  long  bones  are 


fldatanals 


Phalofufef 


Fig.   132. — The   bones   op 

THE  FOOT 
(Thompson) 


260  ADVANCED  PHYSIOLOGY 

not  wasted  spaces  but  are  filled  with  a  soft  yellowish-red  sub- 
stance called  marrow.  In  addition  to  much  fat,  this  ma- 
terial contains  little  bodies  known  as  marrow  cells,  which,  as 
has  been  pointed  out,  produce  red  blood  corpuscles. 

Composition  of  Bone. — Bone  itself  is  composed  of  two  very 
different  substances:  (1)  mineral  substance,  chiefly  phosphate 
of  Hme,  which  is  hard  and  brittle,  and  gives  rigidity;  this  is 
secreted  by  cells  called  osteoblasts,  and  constitutes  about  35% 
of  the  entire  body  substance;  (2)  animal  matter,  a  tougher 
material  than  lime,  and  neither  hard  nor  brittle.  Being  par- 
tially made  of  organic  materials,  when  a  bone  is  placed  in  the 
fire  the  animal  matter  is  burned  away,  leaving  the  lime  only. 
The  animal  matter  gives  strength  and  toughness  to  the  bone 
so  that  it  is  not  easily  broken ;  this  substance  is  called  collagen 
and  makes  up  about  16%  of  a  bone.  Collagen  is  more  familiar 
as  the  material  which  gives  rise  to  gelatine  when  bones  are 
boiled.  The  rest  of  bone  material  (about  50%)  is  chiefly 
water. 

Bones  of  Children  and  Adults. — The  relative  amount  of 
animal  matter  in  the  bones  of  children  is  much  greater  than 
in  those  of  adults.  Indeed,  in  very  early  childhood  the 
bones  consist  wholly  of  animal  matter  and  it  is  not  until 
later  that  lime  is  gradually  deposited  in  them;  the  bones  of 
children  can  therefore  be  bent  considerably  without  breaking. 
This  is  a  manifest  advantage,  for  the  numerous  falls  and  mis- 
haps which  a  child  suffers  would  produce  many  disastrous 
results  were  the  bones  as  brittle  as  in  later  life.  But  for  this 
very  reason  it  is  necessary  that  the  child  be  taught  habits  of 
holding  the  body  erect  and  in  proper  position.  If  the  body 
is  habitually  allowed  to  stoop,  or  assume  a  position  which 
keeps  the  bones  bent  out  of  their  proper  form,  they  will  be 
almost  certain  to  retain  this  shape  when  the  lime  is  deposited 
in  them  and  they  become  hardened.  A  good  straight  form  with 
erect  shoulders  adds  much,  not  only  to  a  person's  appear- 
ance but  also  to  his  health  and  consequent  happiness  in  life. 


THE  SKELETON  261 

Any  kind  of  dress  which  presses  upon  the  bones  is  sure  to 
result  in  deformity.  If  one  wishes  health,  he  should  let  his 
body  grow  as  nature  intended  and  not  curb  it  by  confining 
it  in  tight  garments.  If  the  boy  or  girl  stands  erect  and  is 
not  hampered  by  constricting  clothing,  the  bones  will  develop 
properly.  The  deformity  of  bowed  legs,  however,  is  not  due, 
as  frequently  supposed,  to  the  fact  that  a  child  has  been 
allowed  to  walk  too  early.  ^'Bow  legs"  are  found  chiefly  among 
poor  children,  and  are  caused  by  a  disease  called  rickets, 
brought  on  by  improper  food  and  lack  of  air  and  sunhght. 

Since  so  much  in  the  way  of  body  strength  and  usefulness 
depends  on  the  perfect  condition  of  the  skeleton,  it  is  simply 
a  matter  of  common  sense  that  care  should  be  taken,  espe- 
cially with  growing  children,  that  the  diet  contain  all  mater- 
ials necessary  for  bone  making.  Milk  and  its  products,  with 
wheat  and  oat  cereals,  are  valuable  in  this  connection. 

Repaii  of  Broken  Bones. — The  animal  matter  in  a  bone  is 
the  only  part  of  it  which  is  alive,  and  it  is  this,  therefore, 
which  effects  its  growth  and  repair.  Each  bone  is  provided 
with  tiny  blood  vessels  which  enter  through  small  openings 
and  then  branch  into  numerous  vessels,  running  in  every 
direction  inside  the  bone  and  furnishing  the  living  parts  with 
materials  for  all  necessary  repairs.  The  bone  is  filled  with 
myriads  of  minute  living  cell  bodies,  called  bone  cells,  which 
have  the  power  of  making  new  bone  material  when  necessary, 
and  thus  of  repairing  broken  bones.  If  a  bone  in  the  body  is 
broken  and  the  ends  are  brought  together,  these  living  cells 
begin  at  once  to  unite  the  two  ends,  and  if  allowed  to  continue 
this  work  undisturbed  for  a  few  weeks,  will  completely  join 
them,  making  the  bone  as  strong  as  ever. 

The  value  of  the  periosteum,  too,  in  this  matter  of  bone 
repair  is  very  great,  for,  being  filled  with  blood  capillaries  it 
can  furnish  new  material.  It  has  even  been  shown  that  the 
periosteum,  if  not  disturbed  when  a  bone  is  taken  out  of  the 
body,  can  replace  all  the  hard  parts  of  the  bone. 


262 


ADVANCED    PHYSIOLOGY 


During  a  period  when  a  bone  is  being  repaired  it  must  be 
kept  perfectly  quiet,  for  any  movement  would  easily  tear 
ap&rt  the  newly  made  materials.  Consequently,  the  surgeon 
always  binds  broken  bones  in  such  a  way  as  to  prevent  motion 
of  the  parts  until  they  are  well  knit  together.  The  setting  of 
a  hone  by  a  surgeon  consists  simply  in  bringing  the  two  broken 
ends  nicely  together  and  then  binding  them  in  proper  position. 
Since  the  animal  matter  in  the  bones  of  children  is  so  much 
more  abundant  than  it  is  in  adults,  it  follows  that  broken 
bones  are  more  easily  mended  in  childhood  than  in  later  life. 
In  more  advanced  years  when  the  amount  of  animal  matter 
is  further  decreased,  the  bones  grow  more  brittle  and  are  more 
easily  broken.  At  the  same  time  they  are  not  so  easily  re- 
paired, because  of  the  scarcity  of  living  bone  cells. 

Microscopic  Structure  of  Bone  Tissue. — Figure  133  shows 
a  very  thin  piece  of  bone  highly  magnified.^   It  consists  of 


Sfoodl/kyseL 


Fig.   133. — Sections  thbough  bone 

^,  cross  section;  B,  longitudinal  section.  Canaliculi  are  the  minute  canals  radiating 
from  the  elongate,  black  areas  (lacunae).     Lamellse  are  not  shown. 

groups  of  concentric  rings,  arranged  around  small  openings. 
These  openings  indicate  the  places  where   canals,   running 


THE  SKELETON  263 

lengthwise  of  the  bone,  and  containing  blood  vessels  have 
been  cut  off;  the  concentric  layers  of  bone  tissue  about 
these  are  called  bone  lamellae.  In  the  living  bone  these 
central  openings  are  occupied  by  blood  vessels.  Arranged 
in  rings  around  the  vessels  between  the  scale-like  layers  of 
the  lamellse,  are  a  large  number  of  small,  lens-shaped  spaces, 
called  lacunae,  each  of  which  shows  numerous  fine  lines  radia- 
ting from  it.  Row  after  row  of  these  little  spaces  appear 
arranged  around  the  central  blood  vessel,  forming  larger  and 
larger  rings  until  they  reach  similar  rings  belonging  to  other 
centers. 

Each  of  the  little  spaces  in  the  live  bone  is  filled  with  living 
matter,  which  is  the  remainder  of  what  was  originally  a  bone 
cell.  Because  of  the  deposit  of  such  mineral  matter  about  it, 
the  original  shape  of  the  cell  has  become  almost  unrecogniz- 
able. The  radiating  lines  are  really  minute  tubes,  canaliculi, 
passing  from  one  row  of  spaces  to  the  next.  Since  each  row 
is  connected  with  the  next,  and  since  the  inner  row,  by  means 
of  the  little  tubes,  is  connected  with  the  central  space  and 
hence  with  the  blood  vessel,  even  the  outer  row  of  spaces  is 
supplied  with  nourishment  derived  from  this  vessel.  It  is  be- 
cause the  bone  possesses  so  many  living  cells,  so  well  supplied 
with  nourishment,  that  it  can  be  so  easily  repaired. 

CARTILAGE 

We  have  noticed  that  the  ribs  are  not  united  directly  to 
the  sternum,  but  that  there  is  a  short  piece  of  softer  material 
at  their  front  ends;  this  material  is  cartilage,  a  substance 
which  forms  an  important  part  of  the  skeleton.  Early  in 
Ufe  most  of  the  bones  are  made  of  cartilage.  Even  in  the 
adult  some  cartilage  still  remains;  e.  g.  the  cushions  between 
the  vertebrae,  the  supporting  pieces  around  the  windpipe 
(Fig.  98),  the  pieces  at  the  ends  of  the  ribs  (Fig.  101),  in  the 
joints,  and  in  the  outer  ear,  which  consists  of  cartilage  covered 
with  skin.     Cartilage,  which  is  flexible  but  very  tough,  is 


264  ADVANCED  PHYSIOLOGY 

much  softer  than  bone  and  can  be  readily  cut  with  a  knife. 
It  differs  from  bone  in  that  it  is  not  suppHed  with  blood 
vessels.  Under  the  microscope  a  thin  piece  of  cartilage 
appears  as  in  Figure  4,  page  14.  The  cells  composing  it  are 
far  apart,  separated  by  much  intercellular  substance. 

When,  in  early  Ufe,  certain  cartilage  masses  begin  to  turn 
into  bone,  the  change  does  not  take  place  throughout  the 
cartilage  uniformly,  but  at  certain  points  only,  called  centres 
of  ossification. 

Cartilage  is  not  so  readily  repaired  as  bone,  but  on  the 
other  hand,  it  is  not  so  easily  broken.  A  broken  rib  is  quickly 
mended  in  a  few  weeks  and  is  as  good  as  ever,  but  if  the  injury 
breaks  or  tears  the  cartilage,  its  mending  may  take  a  long 
time. 

JOINTS 

When  two  bones  are  fitted  together  in  such  a  way  that 
there  is  no  movement  between  them,  as  for  example,  the 
bones  of  the  cranium,  the  line  of  joining  is  generally  called 
a  suture  joint;  where  movement  is  possible,  a  joint  is  said 
occur.  Of  the  true  joints  there  are  two  kinds,  imperfect  and 
perfect. 

Imperfect  joints  are  those  in  which  the  bones  concerned  do 
not  actually  glide  over  one  another  although  a  certain  amount 
of  movement  is  possible  because  of  the  flexibility  of  the  elastic 
cartilage  between  them.     Such  joints  are  noticed  where  the 
front  ends  of  the  ribs  approach  the  sternum;  movement  takes i 
place  at  every  breath,  though  it  involves  only  bending  the^ 
cartilages  which  occur  there.     The  bending  and  slight  torsion 
which  may  take  place  between  any  two  vertebrae  also  illus- 
trate the   action   of  imperfect  joints.     Perfect   or  movable 
joints  are  the  sort  generally  thought  of  as  joints  and  occur j 
where  the  end  of  one  bone  actually  turns  on  some  part  of  the] 
surface  of  another. 


THE  SKELETON  265 

As  will  be  pointed  out  later  (page  275),  the  muscles  which 
produce  bending  are  not  necessarily  located  near  the  joint 
they  operate;  such  an  arrangement  would  often  result  in  a 
difficult  and  bungling  sort  of  movement. 

Since  accidents  at  movable  joints  are  always  likely  to  be 
serious  because  they  are  apt  to  cause  stiffness,  we  shall  ex- 
amine one  or  two  carefully  in  order  to  learn  their  mechanism. 
Perfect  joints  are  of  several  different  kinds,  but  most  of  them 
are  modifications  of  three  simple  types:  the  hinge  joint,  the 
ball-and-socket  joint  and  the  pivot  joint. 

The  Hinge  Joint. — In  the  hinge  joint  the  bones  are  able  to 
move  back  and  forth  in  one  direction  only,  like  a  door  on 
hinges:  the  knee,  the  elbow  and  the  joints  of  the  fingers  are 
good  examples.  Since  all  hinge  joints  are  very  much  alike 
in  structure,  the  description  of  one  will  show  the  salient 
features  of  all. 

The  knee  joint  is  made  up  of  the  femur  and  the  tibia  bones; 
Fig.  131.  The  lower  end  of  the  femur  is  large  and  rounded 
in  one  direction  at  the  end,  while  the  upper  end  of  the  tibia  is 
sHghtly  hollowed  on  top;  when  the  bones  are  placed  together, 
their  shape  permits  movement  only  in  one  direction.  The 
rounded  ends  of  both  bones  are  covered  with  a  thin  layer  of 
cartilage,  making  movement  easier.  Two  separate  ring-like 
cartilages,  the  semi-lunar  fibro-cartilages,  one  on  the  outside 
and  one  on  the  inside  of  the  leg,  furnish  extra  padding  to 
relieve  the  body  of  jars,  and  also  fill  up  the  spaces,  making 
the  joint  more  compact.  In  the  living  joint,  there  is  wrapped 
around  the  ends  of  the  bones  the  synovial  membrane,  which 
secretes  into  the  joint  a  liquid,  the  synovial  fluid,  the  purpose  of 
which  is  to  moisten  the  surfaces  and  prevent  friction.  The 
free  motion  of  the  joint  is  dependent  upon  the  presence  of 
this  fluid  and  if  for  any  reason  the  membrane  ceases  to  secrete 
it,  friction  develops,  motion  becomes  difficult,  inflammation 
sets  in,  and  eventually  the  bones  are  likely  to  grow  together 
aft4  the  joint  to  become  stiff.     All  of  the  parts  are  evidently 


266 


ADVANCED  PHYSIOLOGY 


designed  to  make  the  movements  of  the  bones  upon  each 
other  smooth  and  free,  with  the  least  possible  friction. 

The  bones  are  bound  together  by  tough  bands  called  liga- 
ments. At  the  knee  joints  there  are  several  (Fig.  134); 
there  is  a  pair  of  short  ones,  the  crucial  ligaments,  run- 
ning directly  between  the  ends  of  the  bones  and  crossing  each 
other  like  the  parts  of  a  letter  X.  More  important  are  those 
outside  of  the  joint  and  extending  over  it  from  one  bone  to 
the  other.     On  either  side  there  is  a  lateral  ligament,  attached 

to  the  femur  and 
extending  down  to 
the  sides  of  the  upper 
parts  of  the  tibia  and 
fibula.  Another,  the 
posterior  ligament,  at 
the  back  of  the  joint, 
is  attached  to  the 
same  bones.  The 
anterior  ligament  (in 
front)  is  different 
from  the  others  in 
having  in  the  middle, 
a  rounded,  flat  disc 
of  bone,  called  the 
knee  cap,  or  patella, 
strengthening  the 
joint  and  protecting 
the  more  delicate 
parts  within  from  injury.  There  is  another,  rather  irregular 
ligament,  called  the  capsular  ligament,  larger  than  the  others 
and  partly  covering  them  all,  like  a  sac  wrapped  around  the 
bones  and  fastened  to  the  lower  end  of  the  femur  and  the 
upper  end  of  the  tibia. 

The  other  hinge  joints  in  the  body  differ  from  that  at  the 
knee  only  in  slight  details.     The  exact  position  and  number 


Fig.  134. — The  knee  joint 

A  shows  the  exterior  ligaments.     B  shows  the  joint 

with  the  external  parts  removed.  (Thompson) 


THE  SKELETON 


267 


Peht'c  Girdle 


of  ligaments  vary  in  them,  and  no  other  joint  has  a  bone  in 
its  ligaments  like  the  knee  cap.  But  they  all  have  the  same 
smooth,  rounded  surfaces,  the  synovial  membranes  and 
fluids,  the  ligaments  and  muscles  to  complete  the  joint, 
and  are  all,  of  course,  bound  together  on  the  outside  by 
the    skin. 

Ball-and-Socket  Joints. — There  are  only  two  typical  ex- 
amples of  ball-and-socket  joints,  one  at  the  shoulder  and  the 
other  at  the  hip.  As  the  name  indicates,  one  bone  in  such  a 
joint  ends  in  a  rounded,  ball-like  head,  while  the  other  pre- 
sents a  concave  socket 
into  which  the  ball  fits. 
In  an  arrangement  of 
this  kind  the  motions 
of  the  bones  are  not 
confined  to  one  direc- 
tion, giving  greater  free- 
dom of  motion,  but  less 
strength,  than  the  hinge 
joint. 

Three  bones  enter  in- 
to the  shoulder  joint, 
though  only  two  of  them 
are  of  much  importance. 
The  humerus,  the  upper 
bone  of  the  arm,  has  at 
its  upper  end  a  good  sized,  rounded  head  fitting  into  a 
socket  made  by  a  concave  part  of  the  scapula;  Fig.  .127 
This  cavity  is  very  shallow  but  in  the  living  body  there  is 
a  little  rim  of  cartilage  around  its  edge,  making  the  socket 
deeper,  and  the  joint,  therefore,  somewhat  more  secure. 

It  will  be  noticed  from  the  figure  that  two  little  projections 
of  the  scapula  hang  over  this  socket:  while  these  do  not  form 
a  part  of  the  socket  proper,  they  protect  it  from  injury  above 
and  in  front.     It  is  evident  that  when  the  arm  bone  is  lifted, 


Fig.  135. — The  hip  joint 


%S  ADVANCED  PHYSIOLOGY 

it  will  soon  hit  these  projections,  and  its  movement  in  that 
direction  will  consequently  be  stopped.  The  round  ends 
of  the  bones  are  rendered  smoother  by  being  covered  with 
cartilage,  as  in  the  hinge  joint,  and  a  membrane  around  the 
joint  secretes  a  synovial  fluid  for  moistening  the  joint  and 
reducing  friction.  The  bones  at  the  shoulder  joint  are  bound 
together  by  ligaments,  but  these  are  not  so  numerous  as  at 
the  knee  joint.  The  only  important  one,  the  capsular  liga- 
ment, is  attached  to  the  scapula  around  the  socket,  and  then 
extends  out  over  the  head  of  the  humerus  in  such  a  way  that 
it  has  a  wide,  extended  fastening  to  that  bone.  It  is  so  loose 
as 'to  make  it  possible  for  the  bone  to  move  in  any  direction 
without  hindrance.  If  it  is  cut  the  bones  come  apart  at 
once. 

The  ball-and-socket  joint  at  the  hip  differs  from  that  at  the 
shoulder,  in  that  the  muscles  are  much  more  massive  and 
powerful  and  the  socket  is  much  deeper.  The  joint  is  thus 
firmer  but  has  less  freedom  of  movement;  Fig.  135. 

Pivot  Joints. — In  the  case  of  a  pivot  joint,  the  two  bones 
concerned  rotate  on  one  another.  In  the  movements  of  the 
head,  for  example,  all  forward  and  backward  tilting  occurs 
between  the  occipital  bone  of  the  skull,  and  the  first,  or  atlas, 
vertebra,  the  joint  there  being  essentially  a  hinge  joint.  All 
turning  from  right  to  left  (not  tilting  from  side  to  side)  occurs 
between  the  first,  atlas,  and  second,  or  axis  vertebra,  one 
bone  rotating  on  top  of  the  other  and  thus  forming  a  pivot 
joint.  The  turning  of  the  radius  bone  of  the  lower  arm  on 
the  end  of  the  humerus  bone  of  the  upper  arm  is  another  good 
example  of  a  pivot  joint;  Fig.  128. 

INJURIES  TO  JOINTS 

There  are  two  kinds  of  accidents,  not  counting  broken 
bones,  which  occur,  and  frequently  occur  together,  in  joints. 
These  are  sprains  and  dislocations. 

Sprains. — A  sprain  is  due  to  the  stretching  of  some  of  the 


THE  SKELETON  269 

ligaments  in  the  joint  to  such  an  extent  that  they  are  more  or 
less  torn,  a  condition  followed  by  considerable  pain  and  in- 
flammation, accompanied  by  swelling.  The  injury  may  be 
only  a  slight  strain  or  it  may  be  a  severe  rupture  of  the  liga- 
ments, more  serious  than  a  broken  bone,  requiring  longer  to 
heal,  and  being  more  likely  to  result  in  permanent  injury. 
The  best  treatment  is  to  place  the  joint  in  the  most  com- 
fortable position  and  then  apply,  first,  hot  water  (as  hot  as 
endurable),  then,  cold  water.  The  joint  should  then  be  tightly 
bound  in  bandages.  It  is  well  to  rest  the  joint,  but  the  im- 
pression that  it  should  not  be  used  until  it  is  healed  is  a  mis- 
taken one,  for  this  is  likely  to  increase  stiffness  and  make  the 
joint  useless  for  a  very  long  time.  Indeed,  a  sprain  heals 
more  quickly  if  the  joint  has  some  exercise,  and  after  a  day  or 
so,  when  the  first  inflammation  has  subsided,  it  should  be 
exercised  frequently,  and  used  as  soon  as  possible.  This 
treatment  is  a  little  painful,  but  it  results  in  making  the  joint 
usable  much  sooner  than  the  old  method  of  completely 
resting  the  joint  until  the  sprain  is  healed. 

Dislocations. — A  dislocation  occurs  when  the  bones  in  a  joint 
are  pulled  out  of  position,  as,  for  example,  when  the  humerus  is 
pulled  out  of  the  socket  at  the  shoulder,  or  the  end  of  the  femur 
is  pulled  out  of  the  depression  in  the  tibia,  in  which  it  naturally 
rests.  The  first  thing  to  be  done  is  to  pull  the  bones  back 
into  position.  This  usually  requires  the  skill  of  a  surgeon, 
unless  the  dislocation  should  occur  in  one  of  the  small  joints 
of  the  finger,  which  is  easily  put  back  into  its  proper  place. 
Since  a  dislocation  is  almost  sure  to  be  accompanied  by  a 
strain  and  rupture  of  the  ligaments,  it  should,  after  the  bones 
ire  put  back  into  position,  be  treated  just  like  a  sprain. 

THE  CARE  OF  THE  FEET 

That  the  feet  may  be  a  source  of  great  discomfort  many 
iople  are  aware;  but  that  health  is  closely  connected  with 
16  condition  of  the  feet  is  not  so  generally  recognized.     To 


^270  ADVANCED  PHYSIOLOGY 

preserve  one's  health,  exercise  is  necessary;  no  one  can  main- 
tain his  body  in  good  condition  for  many  years  without  it. 
It  is  difficult  to  think  of  any  real  exercise  in  which  the  feet  do 
not  take  some  part.  Walking,  which  is  about  the  mildest 
form  of  exercise,  is  of  course  absolutely  dependent  on  the  con- 
dition of  the  feet.  If  they  are  uncomfortable  when  one 
stands  or  walks  he  will  stay  at  home  as  much  as  possible,  or 
will  use  conveyances  instead  of  his  own  muscles.  He  will 
become  more  and  more  indisposed  to  exercise  and  out-door 
life  generally,  and  his  health  will  inevitably  suffer.  As  much 
attention  should  therefore  be  paid  to  foot  wear  as  to  clothing 
for  other  parts  of  the  body,  and  there  is  no  reason  why  one 
should  not  retain  through  life  feet  which  will  be  a  comfort, 
instead  of  a  painful  hindrance  and  an  agent  limiting  him  in 
all  his  physical  activities. 

Climate  and  modern  customs  compel  us  to  wear  shoes, 
but  the  barefooted  child  of  summer  time  is  still  the  one  who 

experiences  the  greatest 
comfort,  and  whose  feet 
teach  us  what  we  all  need 
to  know  as  to  the  shape 
of  shoes.  Fashion,  rather 
than  health  or  comfort, 
has  dictated  the  shapes 
Fig.  136.— The  bones  and  ligaments  of  our  shoes,  and  there 
OF  THE  FOOT  are  few   people    who    do 

To  show  the  arch  of  the  instep.  (Modified  from       ^^^  ^^^^j.  '^^  consequeUCe. 
Thompson)  * 

Practically  all  defective 
feet,  save  those  improperly  shaped  from  birth,  are  due  to 
badly  patterned  footwear. 

All  common  troubles  of  the  feet  have  to  do  either  (1)  with 
the  skin,  or  (2)  with  the  bones  and  Hgaments  in  the  foot  skele- 
ton. The  most  common  skin  deformities  causing  pain  are 
corns  and  bunions.  Even  though  the  shoe  is  properly 
shaped,  if  it  fits  too  loosely  or  too  tightly,  corns  are  the  al- 


THE  SKELETON  271 

most  inevitable  result.  If  the  shoe  is  too  tight,  a  slight 
amount  of  rubbing  will  irritate  the  skin  and  provoke  the 
growth  of  corns;  if  the  foot  moves  inside  the  shoe  at  each 
step^  it  of  course  rubs  on  the  leather,  and  in  nature's  effort 
to  counteract  this,  a  callous  spot  is  formed  which  grows  con- 
stantly thicker.  Tight  and  badly  shaped  shoes  have  a  still 
more  unfortunate  effect  on  the  small  bones  of  the  toes  and 
ankle,  forcing  these  into  unnatural,  strained  positions.  To 
appreciate  this,  the  free,  unconfined  foot  should  first  be 
studied.  Between  the  heel  and  the  ball  (Fig.  136),  the  fool 
does  not  touch  the  ground,  save  along  its  outer  border  and 
there  only  slightly.  Moreover,  on  the  ball  of  the  foot  the 
weight  falls  largely  on  the  sides,  i.  e.  just  back  of  the  grea 
and  little  toes.  There  is,  thus,  one  longitudinal  and  one 
transverse  arch  in  the  foot.  These  act  as  springs:  when  one 
steps,  the  weight  of  the  body  is  first  thrown  on  the  long  arch 
(on  the  one  between  the  heel  and  the  ball);  as  one  rises  on 
the  toes  in  going  forward,  the  weight  is  transferred  to  the 
transverse  arch;  and  as  it  flattens,  the  foot  should  be  able  to 
spread  a  little,  and  all  the  toes,  each  separately,  to  take  an 
active  part  in  pushing  the  load  ahead. 

It  is  thus  very  easy  to  see  what  high  heeled  shoes  mean  to 
the  long  arch;  they  mean  that  the  weight  will  be  thrown  for- 
ward onto  the  ball,  the  Hgaments  at  A  (Fig.  136)  will  be 
strained,  and  all  the  bones  in  the  ankle  will  be  forced  into 
unnatural  positions  with  consequent  strain  on  those  liga- 
ments. In  connection  with  the  long  arch  it  should  also  be 
j  noticed  that  if  one  "  toes  out ''  excessively  in  walking,  the 
1  weight,  as  one  leans  forward,  is  thrown  on  the  inner  side  of 
i  the  long  arch,  which  has  no  support  at  all,  save  that  of  the 
muscles  and  ligaments.  The  weakening  of  the  ligaments  or 
;  muscles  concerned  in  the  long  arch,  whether  through  badly 
j  shaped  or  high  heeled  shoes,  faulty  position  of  the  feet,  oi* 
I    lack  of  exercise,  leads    to    a   very  Dainful  condition  called 


272  ADVANCED  PHYSIOLOGY 

foot  down  flat  on  the  ground  and  causing  the  nerves  and 
muscles  to  suffer  .much  under  unnatural  strains. 

To  avoid  the  misfortune  of  a  flat  foot  one  needs  to  acquire 
the  habit  of  "toeing  in"  slightly.  If  a  person  practices  rising 
on  the  toes  a  few  times  each  day,  and  in  thus  rising  throws  the 
weight  first  on  the  little  toes  and  then  on  the  great  toes,  and 
also  learns  a  method  of  walking — like  the  Indians — with  toes 
pointed  straight  forward  or  a  little  inwards,  he  will  generally 
avoid  ''flat  foot"  and  broken  arches.  This  method  of  walking 
is  best  acquired  by  throwing  the  hips  slightly  forward  with  each 
step. 

Narrow-toed  shoes  affect  the  transverse  arch  in  front.  If 
the  toes  forming  this  arch  are  crowded  and  confined,  there  is 
nothing  for  them  to  do  but  to  press  mechanically  upon  one 
another  or  be  displaced;  and  when  the  weight  is  thrown  for- 
ward on  the  toes,  if  these  cannot  spread,  they  bind  or  are 
forced  to  cross  one  another. 

A  tight  shoe  incidentally  interferes  with  circulation  in  the 
foot,  which,  of  course,  means  the  inadequate  nourishing  of 
all  the  tissues  concerned,  and  in  winter  especially  makes 
cold  feet  inevitable.  Discomfort  in  any  part  of  the  body 
signifies  that  there  is  nervous  irritation  there,  and  waste  of 
nerve  energy  in  any  one  organ  means  that  less  will  be  avail- 
able for  the  rest  of  the  body. 

A  healthful  shoe  should,  therefore,  have  low  heels,  should 
conform  to  the  shape  of  the  foot,  should  not  be  so  tight  as 
to  pinch,  should  be  made  of  yielding  upper  leather  so  that 
the  toes  may  be  moved,  and  should  fit  in  such  a  way  that  the 
"  breaking  in  "  of  the  shoe  will  not  be  a  necessary  and  dreaded 
experience.  Common  sense  and  public  sentiment  are  de- 
manding that  such  shoes  be  manufactured  more  and  more 
extensively  nowadays,  and  they  can  be  obtained  if  one  will 
insist  upon  comfort  and  health,  instead  of  fashion  and  false 
notions  of  elegance. 


CHAPTER  XVII 


MUSCLES 


C/avK/e 


While  the  skeleton  is  the  hardest  part  of  the  body,  it  is  not 
the  most  abundant  tissue  and  does  not  require  so  large  a  part 
of  the  food  materials  for  its  building  or  maintenance  as  do 
the  muscles.  The  skeleton  gives  the  body  its  general  shape, 
but  the  bones  are  of  use  only  because  of  the  muscles  attached 
to  them.  Life,  of  course,  could  not  continue  if  we  lacked 
the  abihty  to  move,  and  even  though  the  internal  organs  of 
breathing  and  circulation  are  in  good  condition,  there  is  no 
more  pitiful  sight  than  that  of  a  person  whose  limbs  are 
withered  or  whose  muscles  are  paralyzed. 

Muscles  make  up  the  heaviest  part  of  the  arms  and  legs, 
of  the  shoulders  and  hips.  They  occur  in  the  trunk  of 
the  body,  both  in 
front  and  behind. 
The  heart,  arteries 
and  veins  are  chiefly 
composed  of  muscle 
tissue;  the  tongue, 
oesophagus,  stomach 
and  intestine  are  also 
largely  muscular.  In 
short,  about  44%  of 
the  whole  body  is 
made  of  muscle  cells, 
and  most  of  the  food 
taken  into  the  body 
is  used  in  building  them  up,   and  in  furnishing  them  ma- 

K rials  on  which  they  constantly  draw  while  doing  work. 
„3 


i//na 
Fig.  137. — The  arm  (Semi-diagrammatic) 

Showing  the  relations  of  the  biceps  muscle.  From 
the  figure  it  is  evident  that  if  the  muscle  contracts 
slightly  the  fore  arm  will  be  lifted  over  a  great 
distance. 


274 


ADVANCED  PHYSIOLOGY 


Although  muscle  is  usually  thought  of  merely  as  muscle, 
there  are  three  different  kinds:  striped,  smooth  or  unstriped, 
and  cardiac.     This  division  is  made  both  on  the  basis  of  their 

microscopic  structure 
and  of  their  mode  of 
action. 


Peci'oralis 


STRUCTURE  OF 
STRIPED  MUSCLE 


"ijluhus 


Striped  muscles  in- 
clude aU  those  over 
which  we  have  con- 
trol, and  which  are 
attached  to  bones. 
A  good  example  for 
study  is  the  biceps 
muscle  in  the  upper 
arm. 

The  biceps   muscle 
is  shown  in  its  natural 
position    in    Figure 
137.    It  is  a  long  mass 
of    flesh,     large    and 
reddish  in  the  middle, 
and    tapering  at  the 
two     ends     into     a 
dense,  whitish  band, 
called  a  tendon.     The 
middle    portion,    the 
muscle     proper,     is 
alone  capable  of  con- 
traction; the  tendon  simply  fastens  the  muscle  to  the  bone. 
A  tendon  is  made  of  the  same  material  as  that  of  which 
ligaments  are  composed;  ligaments  unite  hones  to  hones,  and 
tendons  unite  muscles  to  hones.     No  muscle  is  united  directly 


Fig. 


Sar^rius 


T38. — The  chief  superficial   muscles 

ON  THE  UPPER  PART  OF  THE  BODY 
(Thompson) 


MUSCLES  275 

to  a  bone;  there  is  always  a  tendinous  tissue  between  them, 
although  it  may  not  be  noticeable.  On  the  other  hand 
the  tendon  may  be  very  long;  for  example,  some  of  the  mus- 
cles which  move  the  fingers  are  near  the  elbow;  Fig.  138. 
The  advantage  of  this  is  obvious;  for  if  the  muscles  were  lo- 
cated in  the  parts  used,  these  would  be  unwieldy  and  large. 
Imagine  the  size  and  awkwardness  of  the  fingers  for  example, 
if  all  the  muscles  concerned  in  their  work  were  located  im- 
mediately in  them.  The  muscles  which  operate  a  bird's  leg 
and  toes  are  placed  high  up  on  the  leg  among  the  feathers. 
The  leg  of  a  wading  bird,  hke  the  flamingo,  is  a  striking  ex- 
ample of  this  contrivance  for  obviating  cumbersome  mechan- 
ism and  allowing  freedom  of  movement.  The  tendons  are 
popularly  called  cords.  The  wrist  is  little  more  than  a  bundle 
of  such  cords  around  the  bones. 

As  Figure  137  shows,  the  upper  part  of  the  biceps  muscle 
is  attached  at  the  shoulder  by  two  tendons  (whence  the 
name  biceps),  while  the  lower  end  is  fastened  by  a  tendon  to 
the  radius  bone  below  the  elbow  joint  but  not  far  from  it. 
A  sHght  shortening  of  the  biceps  will,  therefore,  lift  the  arm 
through  considerable  distance. 

Microscopic  Structure  of  Striped  Muscle. — If  a  muscle  be 
cut  across,  it  will  be  found  to  consist  of  small  parts,  called 
fasciculi,  closely  bound  together,  and  giving  a  "  grain  "  to 
the  muscle  like  that  in  a  piece  of  raw  steak.  If  one  of  these 
fasciculi  be  pulled  to  pieces  and  examined  with  a  microscope, 
it  will  be  found  to  consist  of  a  large  number  of  minute  threads, 
or  fibres;  Fig.   139. 

These  muscle  fibres,  which  are  too  small  to  be  seen  with 
the  naked  eye,  always  run  lengthwise  but  do  not  usually 
extend  the  whole  length  of  a  muscle.  These  fibres  are  cylin- 
drical bodies,  traversed  by  fine  cross  lines,  or  striae,  which 
gives  rise  to  the  name  "  striped  muscle."  Each  fibre  consists 
of  an  outer  tube,  the  sarcolemma,  and  a  jelly-like  substance 
within.     It  is  this  soft  material  in   the  tube  which  is  the 


276 


ADVANCED    PHYSIOLOGY 


Muscle  Fibre 


active  part  of  the  muscle,  the  sarcolemma  itself  having  noth- 
ing to  do  with  its  movement.  A  muscle,  therefore,  con- 
sists of  thousands  of  minute 
fibres,  each  able  to  contract, 
bound  together  in  bundles  to 
form  fasciculi. 

Tendons,  ligaments,  sarcolem- 
ma, periosteum  — ■  all  belong  to 
the  body  material  called  connec- 
tive tissue.  It  is  always  fibrous 
or  membranous  in  structure,  and 
is  so  abundant  that  it  has  been 
said  that  if  all  other  tissues  were 
dissolved  away,  the  shape  of  the 
body  would  still  be  perfectly 
preserved. 

Blood  Supply  to  Muscle. — Into 
each  muscle  enter  one  or  more 
arteries  which  divide  into  minute 
branches  and  finally  end  in  a  set 
of  capillaries  (described  in  a  pre 
vious  chapter;  Fig.  80).  In  this 
way  each  individual  muscle  fibre 
is  in  contact  with  blood  vessels 
and  from  them  obtains  its  nour-j 
ishment — necessitated  by  the 
activity  of  the  muscles.  If  ai 
muscle  is  soaked  in  water  for  a 
while,  the  blood  will  filter  out  and 
leave  the  muscle  nearly  white. 
Contraction  of  Striped  Muscle. — When  a  muscle  contracts 
the  two  ends  are  simply  drawn  toward  one  another,  while  a 
corresponding  swelling  occurs  at  the  middle  of  the  fibre.  The 
muscle  does  not  really  become  any  smaller,  but  merely  shorter 
and  larger  around;  Fig.  140.  It  is  evident  from  Figure  137  that 


NucUm  i^ 


I 


Tendon  t,     mi- 

Fig.  139. — Two  muscle  fibres 

With  tendon  fibres  attached  at  their 
ends. 


MUSCLES 


277 


the  shortening  of  the  muscle  will  lift  the  arm.  After  the  arm 
J  has  been  thus  lifted,  the  muscle  may  remain  contracted  for 
a  time  and  the  arm  held  up,  but  it  requires  a  constant  effort 
to  keep  the  muscle  contracted,  and  just  as  soon  as  the  effort 
ceases,  the  arm  falls  of  its  own 
weight.  The  muscle  has  no 
power  of  forcibly  lengthening 
and  pushing  the  arm  down,  but 
as  the  arm  falls,  it  pulls  out  the 
muscle  to  its  elongated  form 
again.  On  the  back  of  the  arm 
is  another  muscle  which  acts  in 
opposition  to  the  biceps,  these 
two  muscles  thus  forming  a  pair, 
each  of  which  produces  an 
action  opposed  to  that  of  the 
other.  They  cannot  both  act 
at  once. 

Nerve  Control  of  Voluntary 
Muscle  Action. — While  there  are 
some  muscles  in  the  body  (the 
heart,  for  example)  which  perform 
very  regular,  apparently  spon- 
taneous contractions,  all  the  body  muscles  are  more  or  less 
under  the  influence  of  nerves,  and  the  striped  muscles  act 
only  when  stimulated  by  the  brain  or  spinal  cord.  It  is 
because  they  are  under  the  control  of  the  will  that  they  are 
called  voluntary  muscles.  If  a  single  muscle  contracts,  it 
produces  motion  of  a  single  bone  in  a  single  direction.  The 
motions  of  the  body  are,  however,  rarely  simple,  but 
generally  very  compHcated.  In  the  process  of  walking 
nearly  a  hundred  muscles  are  first  contracted  and  then 
relaxed  in  regular  order.  In  throwing  a  baseball,  nearly 
all  of  the  three  hundred  muscles  of  the  body  are  brought 
into    use    to    some    extent,    and    the    remarkable   thing   is 


Fig.    140.— Diagram 

Showing  that  the  muscle  shortens 
though  it  does  not  change  its  bulk 
when  it  contracts. 


278  ADVANCED   PHYSIOLOGY 

that  each  muscle  must  be  contracted  to  just  the  right 
amount  at  just  the  right  moment,  or  the  ball  will  go 
wide  of  the  mark.  To  insure  the  harmonious  action  of  all 
these  muscles  so  that  the  ball  will  go  exactly  where  it  is  in- 
tended, requires  a  most  wonderful  control.  One  does  not, 
of  course,  have  any  consciousness  that  he  is  regulating  all 
these  muscles.  He  simply  decides  to  throw  the  ball,  but  the 
brain  unconsciously  so  regulates  the  stimuli  sent  to  the 
muscles  that  they  act  in  the  order  to  produce  the  desired 
result.  "Practice  makes  perfect,"  simply  because  the  brain 
has  had  the  opportunity  of  learning  to  exercise  this  wonder- 
ful control  over  the  actions  of  the  numerous  muscles. 

Tetanus  of  Striped  Muscles.  — The  term  tetanus,  although 
not  so  familiar,  has  much  the  same  meaning  as  the  word 
"cramps."  When  one  keeps  a  muscle  contracted  as,  for 
instance,  when  he  holds  a  weight  at  arm's  length,  he  does 
this  by  sending  stimuli  into  the  muscles  very  rapidly,  ten  to 
twenty  per  second — so  rapidly  that  the  muscle  does  not  have 
time  to  relax  between  the  successive  stimuli.  As  long  as 
these  stimuli  continue,  the  muscle  remains  contracted,  i.e.  in 
a  condition  of  tetanus.  All  of  our  muscle  actions  are  really 
of  this  character.  Sometimes,  when  a  muscle  is  tired  and 
perhaps  quickly  cooled  by  plunging  into  cold  water,  it  is 
thrown  into  a  similar  state  of  contraction  or  tetanus  without 
one's  willing  it  or  being  able  to  stop  the  contraction.  We 
then  call  it  "  cramps,"  but  it  does  not  differ  from  ordinary 
tetanus,  except  that  it  is  not  voluntary. 

Effects  of  Heat  and  Cold  on  Muscle  Action. — A  jockey 
drives  his  horse  a  couple  of  miles  or  so  before  putting  him  into 
the  race  '^  to  get  him  warmed  up,"  and  athletes  for  the  same 
reason  take  some  gentle  exercise  before  undertaking  the 
actual  contest. 

Whether  the  benefit  of  these  preliminary  exercises  is 
really  due  to  the  warming  of  the  muscles  or  to  an  increased 


MUSCLES  279 

circulation  may  be  open  to  question,  but  there  is  no  doubt 
that  muscles  function  best  when  warm.  Experiments  with 
cold  blooded  animals,  like  the  frog,  show  that  their  muscles 
will  contract  and  relax  five  times  as  rapidly  when  warm  as 
when  cold.  When  cooled  to  40°  F.,  they  will  not  contract  at 
all,  a  condition  known  as  cold  rigor.  On  the  other  hand,  if 
raised  to  a  temperature  much  above  104°  F.,  they  become 
stiff  and  will  not  contract,  a  condition  called  heat  rigor. 
The  effect  of  heat  upon  the  muscles  of  warm  blooded  animals 
is  essentially  the  same.  The  numbness  of  the  human  muscles 
when  chilled  excessively  is  an  illustration  of  the  effect  of  cold 
which  has  come  within  the  experience  of  almost  everyone.  The 
muscles  of  warm  blooded  animals  can  contract  at  a  somewhat 
higher  temperature  than  can  those  of  the  cold  blooded  variety, 
and  it  does  not  take  so  low  a  temperature  to  stop  their  action. 

Fatigue  of  Striped  Muscles. — When  one  is  tired  and  it  be- 
comes more  and  more  of  an  effort  to  make  the  muscles  of  the 
body  contract  and  accomplish  tasks,  it  is  not  primarily  due 
to  the  fatigue  of  the  muscles  themselves  but  to  that  of  the 
nerves.  The  muscle  itself,  however,  on  account  of  changes 
which  take  place  in  it  after  doing  a  large  amount  of  work  may 
become  fatigued.  The  factors  which  enter  into  the  phe- 
nomena of  fatigue  are  not  all  thoroughly  understood,  but  a 
common  supposition  that  weariness  in  muscles  is  relieved  by 
merely  feeding  them,  by  stopping  for  a  meal,  for  instance,  is 
certainly  erroneous.  Not  only  is  the  food  not  at  the  dis- 
posal of  the  muscle  for  a  period  of  several  hours  after  it  is 
eaten,  but  it  has  been  proved  that  a  muscle  can  recover  to 
a  considerable  extent  from  fatigue,  even  when  no  blood  at  all 
is  flowing  through  it. 

Main  Voluntary  Muscles  in  the  Body. — Figure  138  shows 
the  distribution  of  some  of  the  principal  muscles  on  the  ex- 
terior of  the  body.  There  are  more  than  three  hundred 
voluntary  muscles,  some  large,  some  small,  some  short  and 
some  long.     They  are  commonly  enlarged  in  the  middle  and 


fe 


280  ADVANCED    PHYSIOLOGY 

fastened  by  tendons  at  the  ends  and  generally  extend  between 
two  bones,  moving  one  upon  the  other  when  they  contract. 
The  muscles  are  generally  arranged  in  pairs,  one  muscle  of 
the  pair  acting  in  opposition  to  the  other.  This  is  necessi- 
tated by  the  fact  that  muscles  cannot  push  the  bones,  their 
sole  power  being  that  of  contraction. 

Muscles  are  usually  so  attached  to  bones  that  a  short  con- 
traction of  the  muscle  will  produce  a  much  larger  movement 
of  the  bone.  For  example,  it  has  been  seen  (Fig.  137)  that 
the  biceps,  by  shortening  an  inch,  will  lift  the  hand  several 
inches.  This  gives  great  freedom  and  quickness  of  motion. 
A  few  muscles,  however,  are  fastened  in  such  a  way  that  the 
muscle  contracts  through  a  greater  distance  than  that  through 
which  the  weight  is  moved;  this  gives  greater  strength,  but  less 
movement.  An  example  of  this  type  of  arrangement  is  seen  in 
the  "calf^  muscle  of  the  leg,  when  one  rises  on  the  toes;  Fig.  2. 

STRUCTURE  OF  UNSTRIPED  MUSCLE 

Unstriped  muscles  include  all  those  in  the  walls  of  the 
oesophagus,  stomach  and  intestine,  those  in  the  arteries  and 
veins  and  in  the  contractile  parts  of  the  kidneys,  ureters  and 
bladder.  Unstriped  or  plain  muscles  are  not  attached  to 
bones  and  are  always  found  in  the  walls  of  hollow  organs. 
Although,  like  striped  muscles,  they  appear  to  act  only  when 
stimulated  by  the  nerves,  they  cannot  be  controlled  through 
the  will  and  are,  therefore,  called  involuntary  muscles.  Since 
they  are  unattached  and  in  sheets,  e.  g.  those  surrounding  or 
running  lengthwise  of  the  oesophagus,  they  have  no  tendons. 

Plain  muscle  is  composed  of  very  small  cells  or  fibres  each 
with  a  single  nucleus;  Fig.  8,  page  16.  One  of  the  greatest 
differences  between  plain  and  striped  muscles  is  in  their  modes 
of  contraction.  Smooth,  or  plain  muscles  contract  very 
slowly,  several  seconds  often  being  required  for  a  single  con- 
traction, and  they  may  remain  contracted  for  some  time. 
Voluntary  muscles,  on  the  other  hand;  act  very  quickly  both 


MUSCLES  281 

when  contracting  and  when  relaxing.  Because  involuntary 
muscles  act  so  slowly  they  are  very  easily  thrown  into  a  con- 
dition of  tetanus.  Indeed,  so  slow  is  their  response  to  stimuli 
that  in  some  forms  of  smooth  muscle,  one  stimulus  in  five 
seconds  is  sufficient  to  prevent  the  muscle  from  relaxing  at  all. 

It  is  a  great  gain  to  us  that  so  many  muscles  as  are  present 
in  the  entire  digestive,  blood,  and  excretory  systems  can  perform 
their  daily  and  nightly  work  without  any  thought  or  bidding 
on  our  part,  and  without  error  in  time  or  rate. 

Curiously,  however,  smooth  muscle  has  a  disposition  to 
act  with  apparent  spontaneity.  If  a  bit  of  the  circular 
muscle  of  the  intestine  of  some  animal  be  cut  out,  hung  up 
by  one  end  and  stretched  by  a  light  weight  attached  to  the 
other,  it  will  very  soon  lift  the  weight  and  then  relax  again. 
The  muscle  makes  these  movements  over  and  over  again 
without  any  stimulus  and  they  continue  until  the  muscle  is 
exhausted  or  until  its  unusual  exposure  results  in  its  death. 

Isolated  from  the  body  in  this  way,  the  muscle  can  plainly 
receive  no  stimulus  from  the  brain,  and,  although  different 
kinds  of  smooth  muscle  act  very  differently  in  this  respect, 
they  all  have  this  power  of  spontaneous  movement  when  en- 
tirely disconnected  from  the  central  nervous  system.  Whether 
or  not  there  resides  among  the  muscle  cells  some  nerve  in- 
fluence which  is  the  exciting  agent  is  still  an  open  question. 

Although  in  many  respects  striped  and  unstriped  muscles 
act  differently,  yet  in  others  their  relations  are  the  same. 
Both  seem  to  require  the  stimulus  of  nerves  to  make  them 
contract  although  in  one  case  the  contraction  is  voluntary  and 
in  the  other  involuntary.  Both  can  be  thrown  into  tetanus 
by  repeated  stimuli.  Both  are  affected  by  heat  and  cold  in 
the  same  way.     Both  become  fatigued  from  long  action. 

CARDIAC  MUSCLE 

The  muscles  of  the  heart  are  unUke  any  others,  although  in 
structure  as  well  as  in  action  they  have  some  points  of  simi- 


ADVANCED  PHYSIOLOGY 


larity  with  striped  and  unstriped  muscles.     The  cells  com- 
posing them  are  an  elongate  rectangular  in   form,    and   the 
fibres  made  up  of  these  cells  show  irregular  striping;  Fig.    141. 
In  its  action  cardiac  muscle  is  unique  in  several  ways;    it 
acts  quickly,  though    not   as   rapidly   as 
the    ordinary    striped    variety.       Unlike 
either    striped    or   unstriped    muscle,    it 
always  contracts  to  its  shortest  possible 
length,  no  matter  how  weak  the  stimulus 
applied  to  it.      It  can  ''beat"  when  un- 
connected with  the  brain,  but  even  then 
it    apparently   depends    for    its   impulse 
upon  nerve  cells  in  its  own  tissue. 

Cardiac  tissue  is  unique  in  that  it  can- 
not be  thrown  into  tetanus.  As  has 
already  been  noted,  this  condition  is 
usually  provoked  by  the  rapid  recurrence 
of  some  stimulus.  In  heart  muscle,  how- 
ever, two  succeeding  stimuli  do  not  pro- 
duce any  larger  contraction  than  one, 
and  if  another  is  applied  just  before 
the  muscle  begins  to  relax,  it  has  no  effect.  As  soon  as; 
the  muscle  really  begins  to  relax,  it  becomes  open  to  stimu- 
lation and  if  irritated  will  begin  a  second  contraction  before 
it  has  fully  relaxed  from  the  first.  Hence,  no  number  of 
repeated  stimuli  can  induce  tetanus  in  cardiac  muscle;  it 
must  begin  to  relax  before  it  becomes  responsive  to  any  out- 
side influence. 

USE  OF  MUSCLES 

Effect  of  Use. — It  is  a  fact  almost  too  trite  for  mention  that 
the  activities  of  both  work  and  play  tend  to  strengthen  the 
body.  But  increased  strength  is  only  one  of  the  benefits 
derived  from  the  use  of  the  muscles.  When  muscles  are 
active,  all  the  other  organs  of  the  body  are  affected,  an(J 


Fig,  141. — Cardiac 
muscle  cells 


MUSCLES  283 

while  the  size  of  the  muscles  is  generally  noted  as  proof  ot 
the  beneficial  effect  of  exercise,  perhaps  greater  stress  should 
be  laid  on  the  toning  up  of  all  the  internal  organs,  which  re- 
sults when  they  have  been  supplying  the  active  muscles  with 
energy  and  clearing  away  the  debris  resulting  from  "wear 
and  tear." 

Unlike  inorganic  substance,  muscle  increases  instead  of 
diminishing  in  size  with  use.  This  is  true  of  other  living 
matter  also,  e.  g.  brains,  which  grow  with  exercise.  No  one 
can  explain  this  characteristic  of  muscle  fibre,  though  it  is 
inherent  in  the  nature  of  the  substance. 

Effect  of  Disuse. — The  result  of  failure  to  use  muscles  is 
just  the  reverse  of  the  effect  of  use,  i.  e.  they  grow  smaller  and 
weaker,  and  less  perfect  control  of  them  is  possible.  Some 
of  the  peoples  of  India  believe  it  a  religious  duty  to  hold 
their  arms  still  and  have  continued  to  hold  them  so  until  they 
have  become  stiff  and  useless,  the  muscles  losing  absolutely 
all  power  of  contraction.  Although  in  civilized  countries, 
one  rarely  sees  such  complete  loss,  a  partial  loss  of  power  is 
common  among  all  classes  of  people.  Children  in  their  play 
are  pretty  sure  to  use  all  their  muscles  and  are  likely  to  de- 
velop them  uniformly,  but  an  adult  is  rarely  as  capable  of 
free  action  as  a  child.  As  one  grows  older  and  becomes 
quieter,  some  of  the  muscles  always  suffer  from  disuse.  If 
he  uses  trolleys  and  elevators,  the  leg  muscles  suffer,  and  the 
adult  may  lose  the  power  to  walk  as  far  as  the  child.  The 
right  hand  is  used  so  exclusively  that  the  muscles  of  the  left 
become  weak.  The  habit  of  sitting  in  comfortable  reclining 
chairs  gives  the  back  muscles  too  little  exercise  and  they 
often  become  so  weak  that  it  is  really  difficult  for  one  to  sit 
upright  for  a  very  long  time  without  some  sort  of  support. 
Some  people  use  the  laughing  muscles  so  seldom  that  at  last 
they  can  scarcely  be  brought  into  action.  Examples  are 
numerous,  for  few  persons  use  their  muscles  in  such  a  way  as 
to   produce   uniform    development.     Every   one   should   re- 


1 


284  ADVANCED  PHYSIOLOGY 

member  that  each  muscle  he  fails  to  use  will  become  weak  and 
degenerate. 

Need  of  Exercise. — The  great  value,  indeed  the  necessity, 
of  exercising  the  muscles  in  order  to  retain  good  health  is, 
therefore,  evident.  It  is  hardly  necessary  to  advise  the 
average  school  boy  or  girl  to  take  exercise,  for  the  plays  of 
childhood  usually  furnish  plenty  of  it.  But  when  the  boy 
or  girl  outgrows  childish  habits,  and  becomes  a  serious  stu- 
dent, or  goes  to  work  at  some  routine  employment,  there  is 
always  the  danger  of  poor  bodily  development.  The  time 
between  childhood  and  maturity  is  the  period  when  sufficient 
exercise  is  especially  necessary  to  force  all  the  muscles  into 
proper,  harmonious  growth.  When  a  person  has  out-of- 
door  work  to  do,  or  indeed  any  work  which  requires  con- 
siderable muscular  activity,  he  does  not  need  to  think  of 
exercise.  But  in  modern  city  life,  young  people  have  com- 
paratively little  opportunity  for  muscular  exercise  and  are 
almost  sure  to  suffer  from  the  lack  of  it  unless  particular 
attention  is  given  to  the  matter.  It  is  for  this  very  reason 
that  gymnasiums  have  been  established  in  schools  and  else- 
where, and  they  should  be  patronized  by  every  person  whose 
business  is  not  such  as  naturally  to  involve  exercise. 

Exercise  should  not  be  violent.     It  is  of  no  advantage  toj 
try  to  lift  heavy  weights,  or  to  do  difficult  feats  in  the  gym- 
nasium.    Indeed,    such   exercise   is   liable   to   injure   youngj 
people.     We  have  noticed  that  the  bones  of  children  are  not 
all  knitted  together,  and  the  severe  strains  from  attempting] 
difficult  exercise  and  lifting  heavy  weights  are  apt  to  do  per- 
manent injury  to  the  incompletely  fused  bones.     Athletic 
contests  are   certainly  useful,   but  the  tendency  nowadays 
toward  excessive  exercise  in  one  line  rather  than  the  general] 
use  of  all  muscles  results  too  often  in  unreasonably  over- 
taxing one's  strength.     Though  the  results  of  the  straining 
may  not  be  evident  until  long  after  its  occurrence,   whenj 
they  do  appear  in  later  life,  the  person  finds  himself  a  per-' 


MUSCLES 


285 


manent  invalid.     Exercise  is  useful  and  necessary,  but  ath- 
letics are  frequently  harmful  in  their  effect  on  the  body. 

Exercise  for  the  Student. — The  person  who  usually  needs 
the  most  emphatic  advice  as  to  exercise  is  the  one  who  is 
ambitious  to  become  a  scholar.  He  much  prefers  to  remain 
at  his  books,  though  he  above  all  others  should  be  the  one 
to  take  regular  recreation.  He  who  studies  all  the  time  is  in 
the  end  outstripped,  even  at  his  studies,  by  the  one  who  plays 
as  well  as  studies.  No  one  can  become  a  scholar  who  neglects 
to  develop  his  body  while  cultivating  his  brain.  He  will  be 
likely  to  find  in  a  few  years  that  he  must  give  up  study  al- 
together because  his  body  has  been  allowed  to  become  we^k 
while  carrying  out  the  dictates  of  his  brain.  Colleges  have 
been  forced  to  make  gymnasium  practice  a  part  of  the  stu- 
dent's regular  work  in  order  to 
counteract  his  tendency  to  shut 
himself  up  with  his  books. 

Kind  of  Exercise. — Exercise  is 
always  most  beneficial  if  it  is 
pleasant;  exercise  merely  for  the 
sake  of  using  muscles  is  sure  to 
become  irksome.  Hence,  games 
of  base- ball  or  tennis,  rowing  or 
bicycling  in  the  country  are 
preferable  to  gymnastics  or  hard 
work  at  a  required  occupation. 
The  mind  needs  its  recreation, 
as  well  as  the  body  its  exercise. 
Out-of-door  games  are  best. 
Bicycling  is  an  excellent  ex- 
ercise, although  attempts  to  take  long  rides  are  mischievous, 
and  the  habit  of  stooping  over  the  handle  bars  and  "scorch- 
ing'^ is  extremely  bad.  Horse-back  riding  and  walking  are 
also  good,  but  walking  for  exercise  should  be  varied  by  some 
running  or  rapid  walking  up  hill,  so  as  to  make  one  somewhat 


Fig.  142. — Diagram 

Showing  the  effect  upon  the  poise 
of  the  body  produced  by  improper 
standing  posture.  The  dotted  line 
represents  the  backbone. 


286 


ADVANCED  PHYSIOLOGY 


Fig.  143. — Diagram 

Proper  and  improper  sitting  postures 


breathless,  for  the  lungs  need  exercise  as  well  as  the  muscles, 
and  a  quiet  walk  does  not  give  them  as  much  as  they  need. 
The  amount  of  exercise  should  be  equivalent  to  at  least  a  three- 
mile  walk  each  day.     When  it  is  possible,  one  should  not  take 

it  till  two  or  three  hours 
after  eating. 

Everyone     admires      a 
person  with  an  erect  car- 
riage and    a    good    form. 
This  always  means  grace 
and   easy  motion,  and  it 
also   means  good   health. 
A  good  figure  is  more  de- 
pendent   upon    the    con- 
tinued use  of  the  muscles 
of  the  whole  body   than 
upon  the  actual  shape  of  the  body.     It 
is  the  constant  exercise  that  they  are 
required  to  take  that  gives  the  West 
Point  cadets  their  splendid  bearing. 

One  of  the  most  common  defects  is 
that  of  round  shoulders;  Fig.  142. 
This  results,  primarily,  from  the  mere 
failure  to  keep  the  shoulders  back  and 
the  head  erect.  Nothing  is  more  fatal 
to  grace  and  good  general  appearance 
than  this  deformity  and  many  a  per- 
son whose  face  is  not  handsome  makes 
a  very  pleasing  impression  because  of 
a  graceful  form  due  to  a  perfectly  up- 
right head.  ''Head  erect,  shoulders 
back  and  chin  in"  are  three  simple 
directions  for  good  carriage.  Standing  and  sitting  erect 
are  the  means  for  developing  a  sound,  handsome  body,  and 
using  hammocks,  recUning  chairs,  and  leaning  against   sup- 


f  iG.  144. — Diagram 

Showing  the  curvature 
produced  by  carrying  a 
parcel  of  books  under  the 
arm.  To  avoid  this  result, 
if  books  are  carried  under 
the  left  arm  one  day, 
t^ey  should  be  carried 
under  the  right  arm  on 
the  next,  and  vice  versa. 


MdSCLES  287 

ports  when  standing  are  the  common  habits  responsible  for 
many  crooked,  wrongly  developed  figures;  Figs.  143  and  144. 
All  powers  that  are  not  used  are  soon  lost,  and  a  perfect  body 
requires  the  harmonious  development  of  all  its  muscles,  without 
the  excessive  development  of  any  at  the  expense  of  others. 

DISEASES  OF  MUSCLES  AND  BONES 

The  tuberculosis  bacillus  sometimes  attacks  the  bones, 
especially  at  the  joints,  producing  serious  conditions  such  as 
hip-disease.  Frequently  a  trouble  called  rheumatism  appears 
around  the  joints  and  interferes  with  their  ready  action. 
It  is  frequently  an  ailment  of  persons  beyond  middle  age, 
though  it  is  not  uncommonly  found  among  young  people. 
Its  cause  is  not  yet  known  nor  any  method  of  preventing  it, 
except  to  avoid  too  rich  a  proteid  diet. 

Tetanus,  commonly  called  lock-jaw,  is  an  extremely  serious 
disease,  which  is  characterized  by  a  peculiar  state  of  the  muscles. 
It  is  caused  by  a  well  known  bacterium  which 
lives  in  the  soil;  Fig.  145.     If  a  person  receives     ""^^^^ 
an  injury  from    an   instrument    that    has    been         ^jA 
lying  on  the  ground,  a  rusty  nail,  for  example,  ' 

some  of  these  tetanus  bacilli  may  enter  through  Fig.  145. — 
the  wound.  Many  cases  of  this  disease  have  Tetanus 
followed  wounds  from  toy  pistols  and  other  fire-  bacilli 
works  on  the  Fourth  of  July.  If  these  bacilli  that^To- 
get  into  the  body,  they  grow  and  multiply,  ^^ce  lock- 
producing  one  of  the  most  deadly  poisons  ^^^* 
known,  which  is  absorbed  by  the  blood  and  carried  over 
the  body.  The  most  noticeable  symptom  is  that  the 
jaw  muscles  contract  so  tightly  that  the  mouth  can- 
not be  opened,  hence  the  name  lock-jaw.  The  muscles 
i  in  the  rest  of  the  body  soon  undergo  a  similar  con- 
traction. The  disease  is  extremely  painful,  and  prac- 
tically always  fatal.  No  sure  remedy  for  tetanus  is  known, 
though  an  antitoxin  somewhat  like  that  used  for  diphtheria 


288  ADVANCED  PHYSIOLOGY 

is  now  used  successfully  in  many  cases.  The  best  method  of 
combating  this  disease  is  by  preventing  it.  If  wounds  are  care- 
fully cleaned  so  that  no  germs  are  left  in  them,  the  danger  is 
removed.  A  deep  wound  made  by  a  dirty  object  should  be 
cleansed  and  disinfected  with  particular  care.  It  is  always  a 
risk  not  to  put  such  a  wound  in  the  charge  of  a  physician. 
The  deeper  the  wound  and  the  more  dirt  which  gets  into  it, 
the  greater  the  danger. 

It  is  becoming  common  procedure  nowadays  to  inject 
with  tetanus  antitoxin  those  who  have  received  deep  wounds 
made  by  dirty  objects,  or  indeed  any  wounds  that  have  not 
been  treated  from  the  start  with  some  disinfecting  agent. 
This  plan  prevents  the  development  of  tetanus  from  such  wounds 
and  is  far  more  likely  to  be  successful  than  to  try  to  cure  a  case 
after  it  has  developed.  Enormous  quantities  of  this  antitoxin 
have  been  used  for  this  purpose  with  the  soldiers  who  have  been 
wounded  in  the  recent  European  war. 


CHAPTER  XVIil 
THE  NERVOUS  SYSTEM 

Without  the  nervous  system,  the  human  body  would  be  in 
the  lamentable  condition  of  a  fully  equipped  factory  with 
plenty  of  willing  workmen,  which  stands  idle  because  of  the 
lack  of  a  manager.  Not  a  motion  in  the  whole  mechanism 
would  be  possible  and  not  an  impulse  or  thought  be  experi- 
enced. If  the  body  were  not  alive,  this  want  of  power  of 
motion  would  be  perfectly  natural,  but  in  the  living  body  this 
helplessness  through  lack  of  direction  is  one  of  the  saddest  of 
sights.  A  yet  sadder  one  is  that  of  a  living  body  showing  a 
large  amount  of  activity,  but  not  properly  regulated.  Such 
a  condition  we  sometimes  see  in  idiots  or  insane  people :  life 
in  plenty,  action  in  abundance,  but  all  ill-applied  and  reach- 
\Qg  no  useful  end.  It  is  as  if  the  factory  were  running  night 
and  day,  burning  coal  and  using  up  material,  but  turning  out 
no  useful  product. 

The  functions  of  the  nervous  system  are  numerous.  It 
must  direct  and  control  all  visible  movements;  it  must  also 
control  many  invisible  activities  lik^  the  secretions  of  glands, 
the  movements  of  the  intestine  and  the  beating  of  the  heart. 
It  is,  moreover,  concerned  with  higher  functions,  such  as 
feeling,  thinking,  remembering,  willing  and  other  mental 
acts,  many  of  which,  though-  frequently  never  apparent  in 
action,  make  up  the  most  important  part  of  our  lives. 

The  central  nervous  system  consists  of  the  brain  and  spinal 
cord,  which  are  not  separate  organs  but  parts  of  the  same 
mass  of  tissue,  and  contain  most  of  the  nerve  cells  con- 
cerned in  the  higher  functions.  The  delicate  structures  of 
the  central  nervous  system  are  placed  within  strong  protect- 
ing bones,  but  that  they  may  have  communication  with  the 

289 


290  ADVANCED  PHYSIOLOGY 

rest  of  the  body,  they  are  connected  with  the  individual 
organs  by  a  network  of  nerves  and  nerve  endings,  which  make 
up  the  peripheral  nervous  system.  In  addition  to  the  central 
and  peripheral  systems,  there  is  a  third,  partially  independent 
collection  of  nerve  fibres  and  cells,  which  is  known  as  the 
sympathetic  nervous  system. 

THE  CENTRAL  NERVOUS  SYSTEM 

The  Brain. — In  all  the  higher  animals,  the  brain  is  present 
and  is  the  seat  of  the  mental  life.  One  can  scarcely  say  that  it 
is  more  important  than  the  heart  or  the  kidneys,  for  without 
any  one  of  them  life  could  not  continue;  but  it  is  the  sole 
directive  agent  of  the  higher  functions. 

The  brain  is  inside  the  skull,  the  bones  surrounding  it  and 
making  up  the  brain  box  being  called  the  cranium.  Where 
the  backbone  joins  the  skull  the  spinal  cord  passes  into  the 
cranium  through  a  large  opening,  the  foramen  magnum. 

Membranes  about  the  Brain. — Apphed  closely  to  the  inner 
surface  of  the  cranium  is  a  tough  lining  called  the  dura  mater. 
This  serves  at  the  same  time  both  as  a  brain  covering  and  a 
sheath,  which  functions  as  the  periosteum  does  in  other  bones. 
Closely  applied  to  the  brain  itself  is  a  thin,  rather  delicate 
covering,  the  pia  mater.  This  follows  the  brain  surface  com- 
pletely, dipping  into  every  groove  and  covering  every  wrinkle. 
The  pia  mater  is  very  full  of  blood  vessels,  and  thus  forms 
both  a  protecting  and  a  nourishing  agent. 

Between  the  dura  and  the  pia  mater  is  a  thin  tubular  mem- 
brane, the  arachnoid,  the  space  within  it  being  filled  with  the 
arachnoid  fluid.  This  serves  the  very  apparent  purpose  of  a 
cushion.  The  brain  is  exposed  to  countless  jars  as  one  walks 
or  merely  moves  the  head,  and  it  is  easy  to  see  how  much  dif- 
ference this  fluid  cushion  must  make  in  saving  this  delicate 
nerve  center  from  wear  and  tear. 

Main  Divisions  of  the  Brain . — All  animals  with  backbones 
show  the  same  brain  parts  as  man.     Assuming  the  brain  to  be 


THE  NERVOUS  SYSTEM 


291 


Cerebrum 


free  from  all  its  coverings  and  looked  at  from  above,  little  is 
seen  but  two  large  hemispherical  masses,  separated  by  a  deep 
fissure.  These  masses  make  up  the  cerebrum,  and  are  called 
the  cerebral  hemispheres.  If  the  brain  is  tilted  forward  so 
that  the  back  part  of  the  cerebrum  is  visible,  there  comes  into 
view  the  cerebellum,  which  also  shows  an  open  groove  be- 
tween its  right  and 
left  halves.  Below 
the  cerebellum  is  the 
medulla,  which  ex- 
tends downward  and 
passes,  without  any- 
special  line  of  separa- 
tion, into  the  spinal 
cord.  These  parts 
are  shown  in  side 
view  in  Figure  146. 
Viewed  from  below 
(Fig.  147),  the  same 
structures  can  be 
recognized,  and  the 
olfactory  or  smelling 
nerves  should  also 
be  noticed  under  the 

front  lobes  of  the  cerebrum.  Going  from  front  to  back, 
observe  next  between  the  two  cerebral  hemispheres  the 
large  optic  nerves  going  to  the  eyes,  the  nerve  from  the 
right  side,  and  the  one  from  the  left  meeting  in  the  middle 
line.  The  place  where  these  fibres  mingle  forms  an  X-Uke 
structure,  called  the  optic  chiasma,  just  beneath  which  is 
the  small,  round  pituitary  body,  whose  function  is  not  ex- 
actly known.  Behind  this,  notice  on  each  side  a  length- 
wise ridge.  These  two  ridges,  which  are  called  the  crura 
cerebri,  converge  backward  until  they  become  the  right 
and   left    halves   of   the   spinal    cord.     Back   of   the  crura 


Cerebelium 


Fig.  146. — The  human  brain 

Shown  from  the  side  with  the  cerebrum  and  cerebellum 
separated  from  each  other 


292 


ADVANCED  PHYSIOLOGY 


^P^''       Olfacfory 


cerebri  is  a  prominent  transverse  band  of  fibres,  the  pons 
Varolii,  which  connects  the  right  half  of  the  cerebellum  with 

the  left,  going  in 
front  of  (ventral  to) 
the  spinal  cord  as  it 
does  so.  Behind  the 
pons  is  the  medulla. 
The  outer  surface 
of  the  brain  in  some 
of  the  lower  animals 
is  perfectly  smooth, 
but  in  man  the  cere- 
brum and  cerebellum 
show  many  furrows 
dipping  into  the  sur- 
face and  separating 
rounded  ridges, 
called  convolutions. 
If  a  number  of  dif- 
ferent specimens  of 
the  brain  were  ex- 
amined, the  main 
convolutions  would 
be  found  to  occur  in 
the  same  relative 
positions  in  each. 
The  cerebellar  con- 
volutions are  always 
much  narrower  than 
those  of  the  cerebrum 
and  are  more  noticeably  arranged  in  groups,  with  the  ridges 

^The  cranial  nerves  are  numbered;  1,  Olfactory;  2,  Optic  (at  their 
place  of  crossing  [optic  chiasmal  the  pituitary  body  is  shown);  3,  Oculo- 
motor; 4,  Patheticus;  5,  Trigeminal;  6,  Abducens;  7,  Facial;  8,  Auditory; 
9,  Glossopharyngeal;  10,  Vagus;  11,  Spinal  accessory;  12,  Hypoglossal. 


^^''"'1"  ipmolCord 

Fig.  147. — The  brain  as  seen  from  below  i 


Cerebrum 


Qraif  matter  or  Corf  en 
Iffhiiernafkr 


Cerebellum 


Medulla 


Fig.  148. — Diagram 

Representing  the  divisions  of  the  brain  as  lying  in  a 
straight  line  and  separated  from  each  other  and 
showing  the  ventricles  within. 


THE  NERVOUS  SYSTEM  .  293 

approximately  parallel  or  concentric,  as  is  shown  in  Figure  147. 

Cavities  in  the  Interior  of  the  Brain. —  The  interest  which 
anatomists  have  felt  in  the  brain  has  led  them  to  make  minute 
studies  of  its  interior,  but  we  shall  notice  only  a  few  points. 
If  the  cerebral  hemispheres  be  forced  apart  at  the 
top,  they  are  found  to  be  joined  together  toward  their 
centers  by  a  large  cross  band  of  fibres,  called  the  corpus 
callosum.  There  are  also  empty  spaces  in  the  brain.  We 
know  that  this  is  true  of  the  larger  bones  but  we  seldom 
think  of  cavities  in  the  brain.  If  we  assume  the  parts  of  the 
brain  to  be  arranged  in  a  straight  line,  one  part  behind  the 
other,  and  the  whole  to  be  cut  in  a  vertical  plane  near  the 
middle,  the  cavities  or  ventricles  will  appear  as  in  Figure  148, 
as  a  continuous  series  from  the  front  through  the  brain  and 
down  the  cord.  It  must  not  be  supposed  that  these  passages 
are  open  cavities,  for  the  sides  of  the  ventricles  are  in  close 
contact  with  one  another.  They  are,  however,  cavities,  just  as 
there  is  a  cavity  in  a  rubber  water  bottle  when  it  is  empty 
even  though  its  sides  are  collapsed.  Just  what  purpose  these 
cavities  serve  is  not  known.  The  fluid  in  them  is  like  that 
between  the  dura  and  pia  mater  coverings,  of  a  thin  watery 
consistency,  and  may  act  in  connection  with  the  blood  from 
which  it  is  derived,  as  a  means  of  nourishing  the  brain. 

Gray  and  White  Matter. —  If  a  part  of  the  brain  be  cut  open, 
its  tissues  will  appear  to  be  of  two  sorts:  on  the  outside  or 
cortex,  is  gray  matter,  and  inside  this,  white  matter;  Fig.  148. 
This  difference  in  color  would  be  in  itself  of  no  consequence  it 
the  microscope  did  not  show  these  layers  to  be  made  up  of  es- 
sentially different  materials.  The  greater  part  of  the  graj 
matter  contains  numerous  nerve  cells,  while  the  white  mattei 
underlying  the  gray,  appears  to  be  made  up  almost  entirely  of 
nerve  fibres,  which  are,  essentially,  outgrowths  from  tha 
nerve  cells.  This  distribution  of  the  white  and  gray  matter 
in  the  different  parts  of  the  brain  will  be  noted  as  each  divi- 
sion  is  considered. 


294. 


ADVANCED  PHYSIOLOGY 


Surface- r  yy..-;. 
of  Braim  i\'ll,^. 


wm 


THE  CEREBRUM  AND  ITS  FUNCTIONS 

The  cerebrum  is  by  far  the  largest  and  most  important 
part  of  the  brain  and  is  the  real  center  of  thinking,  perceiving, 
willing    and    indeed    of    consciousness.     Its 
primary  activities  are  carried  on  by  the  nerve 
cells  located  in  the  gray  matter  or  cortex. 
The  most  important  experiences  in  our  lives 
are  carried  on  through  the  activities  of  these 
cells.     It  is  much  easier  to  think  of  cells  of 
protoplasm   as   giving  rise  to  materials  like 
iS;i\*/i         saliva  or  bile,  than  to  imagine  them  making 
I  '1m'i4*         thoughts.     The  former  process  is   called  se- 
IiVhA          cretion;  but  shall  we  speak  of  the  cells  of  the 
brain  as  ^'secreting"  or  "making"  thoughts, 
or  as  "containing"  memories,  which  may  be 
drawn  on  at  will?    We  do  not  know;  but  we 
do  know  that  it  is  these  cells  that  are  the  real 
thinking  part  of  the  body. 

Figure  149  shows  a  section  of  the  cortex. 
It  will  be  noticed  that  the  cells  are  of  several 
different  kinds  and  shapes,  though  very  few 
are  round  and  nearly  all  have  several  angles 
or  corners  from  which  extend  and  branch 
thread-Hke  outgrowths,  called  dendrites;  Fig. 
11,  page  18).  There  is  always  one  process 
from  each  cell  that  extends  much  farther 
than  the  others  and  finally  ends,  either  near 
dendrites  of  other  cells,  or  else  passes  down  the 
spinal  cord.  This  long  outgrowth  becomes  the 
central  axis  of  a  nerve  fibre,  over  which 
messages  are  either  sent  or  received  as  the  case 
may  be,  sometimes  for  as  great  a  distance  asj 
two  or  three  feet.  Further  description  of  these] 
nerve  cells  will  be  made  later  (page  310). 


F  I  G.      149.— A 

SECTION  O  F 
THE  CEREBRAL 
CORTEX 
To  show  the  nu- 
merous cells  that 
it  contains.  The 
surface  of  the 
brain  is  at  the 
top  and  the  white 
matter  would  be 
at  the  bottom  of 
the  figure. 


THE  NERVOUS  SYSTEM 


Since  the  white  matter  consists  of  fibres  and  the  g;ray  of 
cells,  the  conclusion  is  that  in  general  the  white  central 
layers  of  the  brain  are 
made  up  of  fibres 
arising  from  the  cells 
that  lie  near  its  sur- 
face. Every  nerve 
fibre  is  really  a  part 
of  a  nerve  cell,  how- 
ever far  from  the  cell 
it  may  extend.  This 
relation  of  the  white 
to  the  gray  matter 
should  be  kept  in 
mind  during  all  our 
discussion  of  brain 
structure  and  func- 
tion. If  the  cells  of 
the  cerebrum  were  in- 
active the  heart  beat 
and  breathing  might 
continue;  but  there 
would  be  no  powers  of 
sensation,  of  thought, 
of  judgment  or  of  vo- 
lition, no  emotions,  no 
anticipation  nor  mem- 
ory; lacking  the  cells 
of  the  cortex  one  could  not  consciously  move  any  muscle  of 
the  body.  Thus,  in  the  cells  of  the  gray  matter  of  the  cerebrum 
reside  all  'powers  of  sensation,  of  voluntary  motion  and  what 
we  call  intellect. 

One  other  very  important  fact  should  be  mentioned  here; 
the  cells  in  the  right  half  of  the  cerebrum  are,  to  quite  an  extent, 
connected  by  fibres  with  the  left  side  of  the  body,  and  those 


Fig.   150. — Diagram 

To  show  the  courses  of  fibres  through  thebrain.  It 
will  be  seen  that  all  paths  to  or  from  the  spinal 
cord  cross,  those  from  the  brain  crossing  at  the 
base  of  the  brain,  and  those  to  the  brain  crossing 
lower  down.  Outer  shaded  area  represents  the 
cortex  of  the  cerebrum;  inner  shaded  areas  are 
subordinate  nerve  centers.   (Landois) 


296  ADVANCED  PHYSIOLOGY 

of  the  left  half  with  the  right  side  of  the  body.  Doubtless  the 
student  has  known  of  a  case  where  some  part  of  a  person's 
body  is  paralyzed.  As  a  rule,  whichever  side  of  the  body 
is  affected,  the  trouble  is  on  the  opposite  side  of  the 
brain.  As  a  proof  of  this,  if  the  brain  of  an  animal  is  laid 
bare  and  then  stimulated  in  spots  with  electricity,  the  move- 
ments which  result  are  always  on  the  side  of  the  body  oppo- 
site to  that  on  which  the  brain  is  stimulated.  Paralysis 
sometimes  results  when  a  blood  vessel  has  broken  and  a  clot 
causes  pressure  on  some  part  of  the  cortex;  if  the  clot  can  be 
removed,  the  patient  may  entirely  recover.  Other  causes 
of  paralysis  will  be  noted  in  connection  with  the  spinal 
nerves. 

The  jSbres  in  the  center  of  the  cerebrum  are  concerned 
wholly  with  carrying  nerve  messages  or  impulses,  never  in 
originating  or  receiving  them.  Figure  150  shows  the  courses 
of  some  of  these  fibres  of  white  matter.  In  the  performance 
of  one's  varied  motions,  it  is  evident  that  the  most  intimate 
connection  between  the  two  sides  of  the  brain  must  be  es- 
tablished. The  right  and  left  sides  of  the  body,  and  both 
arms  and  legs  are  doing  things  which  must  be  directed  toward 
the  same  end  in  an  orderly  manner.  The  figure  shows  that 
some  fibres  put  the  two  halves  of  the  cerebrum  into  com- 
plete communication  with  one  another.  The  different  cells 
of  the  same  side  are  also  connected  since  they  govern  such 
different  muscles  and  must  be  completely  harmonized  in  their 
actions.  No  picture  can  represent  accurately  all  of  these 
fibres,  nor  would  it  be  possible  to  follow  them  all,  so  numerous 
are  they.  It  is  necessary  merely  to  keep  in  mind  that  these 
cells  are  all  in  ready  communication  with  one  another,  and 
thus  work  together  in  the  control  of  the  thousands  of  muscle 
movements  in  the  body. 

Cerebral  Localization. —  The  use  of  these  fibres  becomes 
very  easy  to  understand  when  we  note  that  certain  parts  of 
the  brain  have  special  work  to  do.      The  functions  of  the  cells 


THE  NERVOUS  SYSTEM 


297 


Fig.  151 — The   brain   of  a  monkey 

Showing  the  parts  of  the  brain  that  control 
movements  of  different  parts  of  the  body. 
(Horsley  and  Schafer) 


of  the  middle,  superficial  part  of  the  cerebrum  have  been  par- 
ticularly investigated  and  it  has  been  shown  that  some  of  these 
control  the  muscles  of  the 
arm,  others  those  of  the 
leg,  those  of  the  neck, 
those  of  the  eye  and  so 
on.  The  whole  surface  of 
the  cerebrum  can  not  be 
mapped  out  in  this  way. 
Figure  151  shows  the  main 
areas  of  the  brain  and  the 
parts  of  the  body  which 
they  control.  All  parts  of 
the  brain  cortex  have  not 
yet  been  proved  to  have 
clearly  defined  uses.  In- 
deed, there  are  on  record 
instances  in  which,  through 
accidents,  parts  of  the 
human  brain  have  been 
removed,  and  yet  the  in- 
jured person  showed  no 
unfavorable  effects,  in  fact, 
almost  entirely- recovered. 


THE  CEREBELLUM  AND 
ITS  FUNCTIONS 

We  have  already  noticed 
that  the  external  surface 
of   the    cerebellum  shows 

great  complex   of   nar- 

*row  ridges,  separated  by 

grooves.      If  this  organ  is 

cut  open,  the  cut  surface  shows,  as  does  the  cerebrum,  the 

white    and    gray    matter,    but    it    is    arranged    somewhat 


Fig.  152. — A  section  of  the  cere- 
bellum 

Highly  magnified.  Some  cells  in  this  organ 
have  especially  long  and  nimaerous  den- 
drites.    (ObeBsteiner) 


298  ADVANCED  PHYSIOLOGY 

differently.  Cells  and  fibres  are  also  the  main  materials  of 
which  the  cerebellum  is  made.  Figure  152  shows  their 
arrangement  diagrammatically.  The  nerve  cells  are  of 
several  kinds,  some  showing  very  complex  and  some  very 
simple  bunches  of  dendrites.  In  every  case,  the  cells  are 
located  near  the  surface,  while  the  fibres  make  up  the 
centre  of  each  lobe. 

The  real  use  of  this  part  of  the  brain  is  not  thoroughly 
understood,  but  there  are  two  main  functions  which  are 
usually  ascribed  to  it:  first,  that  of  a  co-ordinating  centre. 
Messages  starting  from  cells  in  the  cerebrum,  on  their  way  to 
the  different  parts  of  the  body,  go  to  the  cerebellum  and  are 
there  brought  together  in  such  a  way  that  the  movements 
which  they  produce  take  place  in  an  orderly,  related  manner. 

In  every  human  being  several  activities  are  going  on  at  the 
same  time.  In  ordinary  walking,  for  example,  the  muscles  in 
one  leg  are  contracting  while  corresponding  muscles  of  the  other 
are  relaxing.  While  a  person  is  walking  it  is  entirely  possible 
for  the  muscles  of  the  neck  to  turn  the  head,  for  those  of  the 
tongue  and  mouth  to  be  concerned  in  speaking,  and  for  those 
of  one  hand  to  be  contracted  about  a  package  or  umbrella. 
Thus,  although  one  does  not  frequently  think  about  it,  all  our 
habitual  activities  involve  a  very  complicated  nervous  mech- 
anism. This  direction  of  movements  so  that  many  muscles 
may  work  together  toward  a  single  end  is  called  co-ordina- 
tion, and  is  one  of  the  functions  of  the  cerebellum.  Impulses 
provoking  movements  start  in  the  cerebrum,  but  are  regulated 
in  the  cerebellum.  An  animal  from  which  the  cerebellum  has 
been  removed  is  unable  to  control  or  direct  the  movements 
of  the  various  body  muscles  and  cannot  perform  even  the 
slightest  action  in  an  orderly,  straightforward  manner. 

A  second  function  of  the  cerebellum  which  has  been  em- 
phasized by  some  physiologists  is  that  of  a  relay  station  for 
outgoing  impulses  from  the  cerebrum,  strengthening  the  force 
of  nerve  messages  on  their  way  to  the  lower  muscles  of  the 


THE  NERVOUS  SYSTEM  SM 

body.  Acts  of  thinking,  too,  seem  to  be  somewhat  weakened, 
becoming  less  virile  and  positive,  in  the  cases  where  the 
cerebellum  has  been  impaired  by  disease  or  some  other  cause. 
However,  this  function  of  the  cerebellum  as  a  message- 
strengthening  organ  cannot  be  regarded  as  so  important,  or 
so  certainly  known,  as  its  co-ordinating  influence. 

THE  MEDULLA 

The  medulla  is  connected  with  the  control  of  respiratory 
and  circulatory  organs.  It  lies  beneath  the  cerebellum  and 
its  lower  end  is  continuous  with  the  spinal  cord  from  which 
it  is  not  distinctly  separate.  Large  bundles  of  fibres,  crura 
cerebri,  extend  from  its  upper  end  into  the  cerebrum. 

If  the  tissues  of  the  medulla  were  carefully  examined,  it 
would  show  a  complex  mixture  of  nerve  fibres  and  nerve  cells, 
whose  arrangement  would  differ  very  much,  depending  on 
whether  the  cut  were  made  through  the  anterior,  middle  or 
posterior  portion  of  the  structure.  We  need  merely  note 
that  among  these  fibres  there  are  patches  of  cells,  sometimes 
called  ''  nuclei,"  from  which  most  of  the  cranial  nerves  take 
their  origin.  The  fibres  themselves  come  from  cells  which 
are  either  in  the  cerebrum  or  lower  down,  in  the  cord;  so  that 
the  medulla  becomes  a  great  complex  of  paths  for  messages 
passing  in  either  direction. 

So  far  as  its  fibres  are  concerned,  the  medulla  simply  trans- 
mits messages  from  the  brain  down  to  the  spinal  cord,  and  in 
the  reverse  direction,  but  its  nerve  cells  give  it  some  other 
functions.  The  particular  activities  which  are  controlled 
by  the  nerve  cells  of  the  medulla  have  been  determined  by 
removing  from  some  animal  the  other  parts  of  the  brain  and 
then  noting  carefully  what  powers  have  been  taken  away  and 
what  powers  are  left.  Such  an  animal  keeps  on  breathing,  and 
the  blood  vessels  still  continue  to  expand  and  contract,  so  we 
say  that  the  medulla  contains  respiratory  and  vaso-motor 
centers.      In  the  medulla  is  also  the  cardio-inhibitory  center, 


300 


ADVANCED  PHYSIOLOGY 


rachial 
P/exus 


from  which  messages  go  over  the  vagus  nerves  to  check  the 
beating  of  the  heart;  see  page  145.     Although  the  above  are 

the  most  important,  there  are  other 
centers  located  in  the  medulla;  but, 
in  general  we  may  say  that  the 
medulla  is  the  seat  of  all  involuntary 
activities. 

THE  CONNECTIONS  BETWEEN  THE 
BRAIN  AND  THE  BODY 


The  brain,  shut  up  as  it  is  within 
the  bony  walled  cranium,  may  be 
compared  to  a  telegraph  operator  in 
his  small  office.  It  is  quite  remote 
from  many  important  organs  of  the 
body,  but  by  means  of  innumerable 
nerve  fibres,  corresponding  to  tele- 
graph wires,  it  is  connected  with 
them  all,  as  the  telegraph  operator 
may  be  in  communication  with  the 
rest  of  the  world.  The  next  step 
in  our  discussion,  then,  is  to  study 
the  spinal  cord,  which  is  the  main 
cable,  as  it  were,  of  nerve  fibres. 


THE  SPINAL  CORD 


Fig.   153. — The  spinal 


Since  the  term  spine  is  commonly 

appHed  to  the  backbone,   the  large 

nerve    which   passes   down   through 

it  is  naturally  called  the  spinal  cord. 

Notwithstanding    the    innumerable 

twists   and   bends   which   the   body 

makes,  the  cord  is  perfectly  protected  from  strain  and  injury. 

Figure  123  shows  that  each  vertebra  is  essentially  an  irregular 

ring  of  bone  encircHng  an  opening;  when  a  number  of  vertebrae 


CORD 
With  the  spinal  nerves   at- 
tached.    Upon    one    side  is 
shown     the    sympathetic 
system.  (Thompson) 


THE  NERVOUS  SYSTEM 


301 


are  arranged  one  on  top  of  the  other,  these  openings  form  a 
long  tube,  the  spinal  canal.  In  this  is  the  spinal  cord,  con- 
tinuous with  the  brain  above  and  terminating  by  dividing  into 
branches  in  the  lumbar  vertebrae.  Fig.  121.  It  is  nearly  uni- 
form in  size  throughout  its  length,  though  it  enlarges  somewhat 
as  it  merges  into  the  brain  and  is  somewhat  larger  than  else- 
where in  the  region  between  the  shoulders  and  in  the  lumbar 
region,  or  "  small  of  the  back.'*  Its  average  diameter  is  about 
three-quarters  of  an  inch. 

Like  the  brain  the  cord  is  protected  by  two  sheaths,  the 
dura  mater  and  the  pia  mater,  which  are  continuous  with 


rPoshnor  Rool^ 


lama 


ier 


Merve 
fibres 


Nerve 

Cells 

or 

Orat/ 

flatter 

AhferiorRoof 

Fig.  154. — A  cross  section  of  the  spinal  cord 

The  white  matter  is  really  filled  with  nerve  fibres  but  in  the  figure  these  are  shown 

at  only  one  point. 

those  of  the  brain,  and  like  them  in  every  way,  save 
that  the  dura  mater  is  not  grown  to  the  vertebrae  as  it  is  to 
the  inner  side  of  the  cranial  bones.  Arachnoid  fluid  is  present 
and  forms  a  cushion  about  the  cord  as  it  does  about  the  brain. 
Structure  of  the  Cord. — The  cord  is  cylindrical  in  shape 
and  divided  into  right  and  left  halves  by  deep  grooves,  one 


302 


ADVANCED  PHYSIOLOGY 


on  its  anterior  and  one  on  its  posterior  surface,  the  anterior 
being  more  open  and  more  shallow  than  the  posterior.  The 
two  halves,  which  are  clearly  shown  in  Figure  153,  are  held 
together  by  a  central  connecting  portion,  about  one  third  of 
the  diameter  in  width. 

The  grooves  of  the  cord  are  still  better  appreciated  by  a 
study  of  a  cross  section;  Fig.  154.  Such  a  section,  too,  shows 
that  the  cord,  like  the  brain,  is  made  up  of  two  kinds  of 
material,  nerve  fibres  and  nerve  cells,  though  in  reversed  re- 
lations, the  outer  layers  of  the  cord  being  of  white,  fibrous 
matter,  and  the  inner  of  gray,  cellular  matter.  Recognizing 
that  the  nerve  fibres  simply  conduct  impulses,  while  the  nerve 
cells  have  other  more  complex  functions,  it  will  be  evident 
that  the  cord  has  these  two  different  classes  of  activities. 
Since  the  process  of  conduction  is  the  simpler  matter,  we  shall 
study  it  first. 

The   Cord   as   a   Conductor  of  Impulses.  — Messages    sent 

through     the     cord     pass 


Pojferior  Roof 


Anierio. 
Hoof 


either  up  or  down  in  the 
white  matter;  but  do  im- 
pulses going  up  the  cord 
follow  the  same  paths  as 
those  going  down?  This 
question  has  been  answered 
by  experiments  on  some  of 
the  lower  animals  which  are 
constructed  essentially  like 
man,  and  also  by  observa- 
tion of  the  results  in  human 
beings  in  which  the  cord  is 
diseased  or  has  been  injured 
by  accident.  These  observa- 
tions have  shown  that  if  a 
part  of  the  cord  is  disabled,  sometimes  sensation  and  some- 


Fig.  155. — Diagram    of    a    cross 
section  of  the  spinal  cord 

Showing  the  parts  that  carry  messages 
up  (ascending)  and   those   that    carry 
messages  down  the  cord  (descending). 
(Modified  from  Flint  and  Landois) 


THE  NERVOUS  SYSTEM 


303 


times  the  power  of  motion  is  lost  below  the  injured  point. 

If  the  power  of  motion  is  lost,  e.g.  the  motion  of  the  leg,  then 

the  injury  must  be  in  a  descending  tract,  where  the  messages 

that  pass  from  the  brain  down  to  the  leg  have  been  interfered 

with.     If  the  person 

loses    the    sensation    of 

feeling  so  that  he  has  no 

consciousness  of  anything 

that   may  touch  a  given 

part  of  the  body  below 

the  injured  spot,  then  it 

is    assumed    that    an 

ascending  tract  has  been 

severed. 

By  these  studies  the 
areas  which  are  devoted 
to  impulses  going  in  one 
direction  or  the  other 
have  been  determined 
approximately  as  in 
Figure  155.  Roughly 
speaking,  all  ascending 
impulses  go  up  to  the 
brain  either  on  the  poste- 
rior side  or  on  the  right' 
and  left  lateral  regions 
near  the  surface;  while 
the  descending  impulses 
pass  downward  on  the  anterior  side  or  in  the  deeper  layers 
of  the  lateral  regions. 

One  unexpected  fact,  however,  comes  to  light  in  studying 
the  nerve  paths  in  the  spinal  cord.  An  injury  on  one  side 
of  the  cord  is,  as  a  rule,  accompanied  by  loss  of  sensation  on 
the  other  side  of  the  body  but  not  on  the  same  side  as  the 
injury.     The  conclusion  is  that  messages  brought  into  the 


Fig.  156. — Diagram 

Showing  the  course  of  the  ingoing  and  outgoing 
impulses  in  the  cord. 


$04 


ADVANCED  PHYSIOLOGY 


spinal  cord  pass  immediately  to  the  other  side  and  ascend 
there.  Curiously  enough,  however,  an  injury  destroys  the 
power  of  voluntary  motion  on  the  same  side  as  the  injury, 
but  not  on  the  other.  Hence  messages  from  the  brain  pass 
down  the  cord  on  the  same  side  as  that  to  which  they  finally 
go.  Figure  156  shoWs  these  facts  diagrammatically.  These 
messages  from  the  brain  going  down  the  cord  cross  over  from 
left  to  right  and  vice  versa,  higher  up,  mainly  in  the  me- 
dulla, so  that  all  messages  going  to  either  side  of  the  body 
start  from  the  other  side  of  the  brain.  Thus,  the  sensations 
and  motions  of  each  side  of  the  body  are  connected  with  and 

controlled  by  the  cells  in 

the  cerebral  hemisphere  of 
the  other  side.  Although 
there  are  a  few  exceptions 
to  this  arrangement,  this 
is,  in  the  main,  the  rela- 
tion of  the  spinal  cord  to 
the  rest  of  the  body. 

THE  PERn>HERAL  NER- 
VOUS SYSTEM 

The  nerves  over  which 
messages   are  brought  to 
the    spinal    cord  or    the 
brain     and     those     over 
which  messages   are  sent 
out  compose  the   periph- 
eral   nervous    system. 
These  nerves  are  classed 
in    two    groups:    (1)    the 
cranial  nerves  which  go  to 
or  leave  the  brain  directly  without  entering  the  cord;   (2) 
the  spinal  nerves  which  enter  and  leave  the  cord. 
The   Cranial  Nerves. — The   cranial  nerves   are  twelve  in 


'  Vagus 
*^"'  fotfearf&Lungt 


Fig.  157. — Diagram 

Showing  the  distribution  of  the  different  cranial 
nerves.  The  numbers  indicate  the  number 
of  each  nerve,  and  the  arrows  show  whether 
each  is  afferent  or  efferent. 


[ 
I 


THE  NERVOUS  SYSTEM  305 

number,  arising  directly  from  the  brain  and  passing  out  of 
the  cranium  to  supply,  chiefly,  the  organs  of  the  head;  Fig.  157. 
The  muscles  of  the  head  are  controlled  by  them,  sensations 
from  the  face,  the  nose,  the  eye,  the  ear  and  the  tongue  are 
received  through  them.  Some  of  the  more  important  of  these 
we  shall  consider  in  the  following  chapter. 

The  Spinal  Nerves,  i — Between  the  neural  arches  of  each 
two  vertebrse  enough  space  is  left  for  a  nerve  of  considerable 
size  to  pass  from  the  spinal  cord  on  each  side.  There  are 
thirty-one    of    these   spinal   nerves  on  PosiaiorJioot 

each  side  of  the  cord.  Five  of  them 
unite  to  make  up  the  brachial  plexus, 
i.e.  the  nerve  combination  which 
supplies  the  arm;  four  form  the  lumbar 
plexus  and  thence  pass  down  each  leg  AmemTRoot 

as  one  nerve;  Fig.  153.  The  rest  supply  Fig.  158.— A  bit  of 
the  numerous  organs  of  the  neck  and  ™^  ^^^^^^  ^^^^ 

,  -^.  icrou  ±u    4.  Showing    the     method    of 

trunk  proper.  Figure  158  shows  that  a  origin,  of  the  spinal  nerves 
spinal  nerve  does  not  leave  or  enter  the  ^y  *^o  ™°*s- 
cord  in  one  place  as  a  branch  grows  out  of  a  tree,  but  arises 
by  two  roots,  one  being  continuous  with  the  gray  matter  in 
the  anterior  part  of  the  cord  and  the  other  with  that  in  the 
posterior  part.  These  two  roots  join  to  form  one  nerve; 
before  their  junction,  however,  a  swelling,  a  nerve  ganglion, 
occurs  on  the  posterior  root. 

The  precise  function  of  these  two  roots  has  been  ascertained 
by  experiments  upon  animals.  If,  for  example,  the  posterior 
roots  of  all  the  nerves  going  to  some  one  organ,  e.g.  the  leg, 
have  been  cut,  it  is  found  that  nothing  touching  the  leg,  not 
even  a  burn,  is  felt  in  the  least,  but  it  is  still  possible  for  the 
animal  to  move  the  leg  or  any  part  of  it.  This  result  shows 
that  all  sensory  impulses,  all  messages  having  to  do  with 
feeling,  as  we  say,  pass  from  the  leg  into  the  spinal  cord  over 
the  posterior  roots  of  the  spinal  nerves.     The  function  of  the 


306 


ADVANCED  PHYSIOLOGY 


posterior  roots  of  all  the  spinal  nerves  of  the  bod}^,  therefore, 
is  to  carry  sensory  messages  or  impulses  which  are  always 
passing  into  the  cord  or  brain,  and  are  frequently  called 
afferent  impulses,  and  the  nerves  concerned,  afferent  nerves. 
If,  on  the  other  hand,  the  ventral  or  anterior  roots  are  cut 
and  the  posterior  left  intact,  the  animal  so  injured  is  unable 
to  move  its  leg,  but  can  feel  perfectly  anything  in  contact 
with  it.      From  this,  one  decides  that  the  impulses  from  the 

brain  or  cord  which  go 
to  the  muscles  of  the  leg 
leave  the  cord  by  the 
anterior  roots.  The  ante- 
rior roots  of  all  spinal 
nerves,  then,  carry  motor 
impulses.  Motor  im- 
pulses always  pass  from 
the  cord  or  brain;  they 
are  called  efferent  im- 
pulses and  the  nerves 
concerned  in  carrying 
them,  the  efferent  nerves. 
After  the  dorsal  and 
ventral  roots  (afferent 
and  efferent)  unite  into 


Fig.  159. — Three  nerve  cells 

In  two  of  them   is  shown   the   axon,  or  axis 
cylinder,  of  the  nerve  connected  with  the  cell. 


a  single  trunk,  the  spinal  nerve  resulting  is  a  mixture  of  both 
kinds  of  fibres,  though  their  functions  remain  distinct.  In 
the  various  figures  in  this  chapter  the  direction  of  the  arrows 
indicates  the  direction  of  the  impulses  that  pass  through  the 
various  nerves.  The  number  of  nerve  fibres  that  thus  enter 
or  find  exit  through  the  cord  is  very  large.  There  are  many 
hundreds  of  thousands  of  them  in  the  thirty-one  pairs  of  spinal 
nerves  and  by  means  of  them  every  part  of  the  body  is  brought 
under  the  direct  influence  of  the  spinal  cord  and  brain. 

Structure  of  Nerve  Fibres. — In    the   opening    chapter   the 
mmute  cells  which  make  up  the  bodv  were  described.     These 


THE  NERVOUS  SYSTEM  307 

cells  are  essentially  alike,  in  that  each  consists  of  a  bit  of  proto 
plasm,  containing  a  nucleus.  Nerve  cells  differ  from  others, 
of  course,  in  their  pecuHar  function,  and  it  would  be  interest- 
ing indeed  to  know  how  they  do  their  work  of  thinking, 
memorizing,  inventing,  etc.,  but  this  no  one  can  tell.  They 
also  frequently  differ  from  others  in  their  very  irregular  shape 
(Fig.  159)  and  in  the  outgi'owth  from  most  of  them  of  a  long 
process,  the  axon,  or  axis  cylinder,  the  work  of  no  other  cells 
requiring  such  connection  with  parts  of  the  body  at  a  dis- 
tance from  them. 

A  portion  of  a  nerve  fibre  is  represented  in  Figure  160.    It 
consists  of  a  very  fine  central  thread,  the  above-mentioned 


I 


^  Primitive  Sh«ath__  fledulfant^ 

Fig.  160. — A  short  piece  of  a  nerve  jtibrb 

Very  highly  magniiiecL 


axis  cylinder,  which  is  continuous  from  its  point  of  exit  from 
a  cell  in  the  brain  or  spinal  cord,  to  its  end,  e.  g.  in  some 
muscle,  gland  or  skin  cell.  Covering  this  axis  cylinder,  which 
is  the  real  conducting  fibre  of  the  nerve,  is  the  medullary 
sheath,  which  is  of  material  different  from  that  of  the  fibre  and 
contains  considerable  fat.  It  seems  to  act  as  a  covering  to 
prevent  impulses  which  are  passing  along  the  fibre  from 
jumping  across  into  other  fibres  lying  close  by,  thus  serving 
something  the  same  purpose  as  does  the  insulating  covering 
of  gutta  percha  around  an  electric  wire.  This  medullary 
sheath  is  interrupted  at  short  intervals  called  nodes  (Fig. 
160)  and  between  every  two  nodes  there  occurs  a  nucleus 
showing  the  medullary  sheath  to  be  made  up  of  many  cells. 
Outside  the  whole  is  a  thin  covering,  the  primitive  sheath. 

On  the  other  hand,   since  this  sheath  contains  fats,  the 
nutrition  of  the  nerve  fibre  has  been  regarded  as  its  main 
ction.    There  is  little  to  support  this  view,  however. 


I 


308 


ADVANCED  PHYSIOLOGY 


Sheath 


Fig.   161. — A  cross  section  of  a 

NERVE 

Showing  it  to  be  a  bundle  of  fibres  held 

in  a  sheath  of  connective  tissue. 


In  the  spinal  nerves  and  every  nerve  leaving  or  entering 
the  brain  or  cord  there  are  very  many  of  these  minute  fibres 
running  together  in  a  bundle.     It  is  this  bundle  of  nerve  fibres 

which  is  meant  when  the  term 
Fibre  nerve  is  popularly  used;  Fig. 

161.  Even  in  the  bundle, 
each  fibre  has  its  medullary 
and  primitive  sheaths;  only 
after  the  fibre  has  entered  or 
before  it  leaves  the  brain  or 
spinal  cord  is  the  primitive 
sheath  left  off.  In  the  white 
matter  of  the  central  nervous 
system  the  fibres  have  unin- 
terrupted medullary  sheaths, 
i.  e.  not  divided  into  nodes 
and  internodes,  and  there  are  no  external  sheaths.  In 
very  exceptional  cases,  as  for  example,  the  nerves  going  to 
the  nose,  which  is  so  near  the  brain,  both  medullary  and 
primitive  sheaths  are  wanting. 

Replacement  of  Nerves  after  their  Injury. — Whenever  a  per- 
son cuts  or  otherwise  injures  the  skin  or  any  muscle  just 
beneath  it,  healing  begins  almost  at  once  and  soon  there  is 
enough  new  tissue  formed  to  repair  the  wound  completely. 
When,  however,  one  of  the  long  nerve  fibres  which  pass  from 
the  cord  or  brain  to  the  surface  of  the  body  is  cut  off,  repair 
takes  place  in  a  very  different  way.  The  two  ends  of  the  cut 
nerve  will  never  come  together  again  and  mend,  but  the  part 
of  the  fibre  between  the  point  of  injury  and  the  organ  to  which 
it  goes  dies.  The  stump  between  the  injured  place  and  the 
cord  or  brain  often  does  not  deteriorate  at  all,  or  only  for  a 
very  short  distance. 

A  new  nerve  to  replace  the  portion  of  the  nerve  peripheral 
to  the  injury  is  formed  from  material  made  by  the  cells  of 
the  old  primitive  sheath.     These  increase  in  number  along 


THE  NERVOUS  SYSTEM 


the  line  of  the  old  fibre,  become  changed  at  first  into  a  jelly- 
like material  and  later  into  nerve-fibre  substance.  This  new 
nerve  fibre  makes  connections  with  the  stump  of  the  old  one, 
and  communication  is  again  possible  between  the  cell  in  the 
cord  or  brain  and  the  old  nerve  ending. 

Nerve  Endings. — As  has  been  pointed  out,  nerves  are  divided 
into  two  classes:  (1)  the  afferent  nerves,  which  bring  in  im- 
pulses from  the  outside  world  or  from  internal  organs  to  the 
spinal  cord  or  brain;  and  (2)  the  efferent  nerves,  which  take 
impulses  out  from  the  cord  or  brain  to  the  organs  which  they 
supply. 

Several  kinds  of  afferent  nerve  endings,  or  more  properly 
beginnings,  in  the  skin  or  elsewhere  have  already  been  re- 
ferred to  and  shown  in  Figures  112,  117  and  118.  In  general, 
they  may  be  said  to  start  in  very  minute  spheres  or  oblong 
bodies  called  corpuscles.  The  nerve  fibrils  begin  here  as  fine 
branches  either   on   the  sx ..Nerve 

exterior  or  in  the  in- 
terior of  these  organs. 
These  skin  end-organs 
receive  mainly  impres- 
sions of  touch  and  tem- 
perature, an  extreme  of 
either  taking  the  form 
of  pain. 

The  efferent  nerves 
are  distributed  almost 
entirely  to  muscles  and 
glands  and  excite  these  to  action.  The  manner  in  which 
nerves  end  in  muscles  is  diagrammatically  shown  in  Figure 
162.  It  is  not  possible  to  say  just  what  happens  in  a  muscle 
or  gland  when  a  message  is  delivered  to  it.  The  muscle 
contracts  or  the  gland  secretes,  but  just  what  change  in  their 
protoplasm  excites  these  activities  is  not   known. 


Fig.  162. — The  ending  of  a  nerve  in 

MUSCLE    fibres 

The  end   organ    of   a    motor    nerve.    (Bohn  «& 

Davidofif) 


CHAPTER  XIX 

THE  NERVOUS  SYSTEM— NEURONS,  NERVE 
IMPULSES  AND  REFLEX  ACTION 

It  has  already  been  noted  that  the  whole  nervous  system  is 
made  up  of  nerve  cells  and  nerve  fibres,  which  indeed  form 
the  basis  of  the  gray  and  white  matter,  respectively.  The 
fibres  and  cells  are  not  separate  structures  but  each  fibre  is 
a  part  of  some  cell;  and  thus  it  comes  about  that  the  whole 
nervous  system  is  composed  of  these  units,  each  consisting 
of  a  cell  with  its  connected  fibre  or  fibres.  These  units  are 
called  neurons  (one  of  these  is  pictured  in  Figure  11).  Each 
consists  of  a  nerve  cell  with  its  nucleus;  extending  from  the 
ceil  are  dendrites  and  one  axis  cylinder,  at  the  distal  or 
outer  end  of  which  is  a  nerve  ending. 

A  neuron  may  receive  an  impulse  through  its  axis  cylinder 
and  send  it  out  through  its  dendrites,  or  it  may  receive  the 
impulse  through  its  dendrites  and  send  it  out  through  its  axis 
cylinder.  In  either  case  it  is  as  the  neurons  act,  each  by  itself, 
and  each  in  connection  with  the  other  neurons,  that  the  func- 
tions of  the  nervous  system  are  performed.  Some  of  them 
constitute  the  thinking  and  willing  part  of  the  brain;  others 
^in  the  cord  and  elsewhere  are  the  servants  of  those  in  the  brain, 
since  they  carry  messages  to  and  from  the  brain,  though  the}^ 
have,  besides,  important  functions  in  connection  with  reflex 
actions.  We  shall  consider  first  those  which  carry  impulses 
to  the  brain,  then  those  that  carry  impulses  away  from  it 
and  finally  those  concerned  in  reflexes. 


NERVE  IMPULSES  AND  REFLEX  ACTION 


311 


THE  NEURONS  AS  TRANSMITTERS  OF  IMPULSES 


Ingoing  Paths. — We  have  already  learned  that  the  pos- 
terior roots  of  the  spinal  nerves  carry  messages  inward  and 
that  upon  each  posterior  root 
there  is  a  swelling,  the  so-called 
spinal    gangUon;    Fig.    158. 

Inside  this  spinal  ganglion  are 
the  cell  bodies  of  a  large 
number  of  neurons.  From  each 
ceil  body  extends  a  single  pro- 
jection or  axis  cylinder,  which 
soon  divides,  one  branch  passing 
inward  to  the  spinal  cord,  the 
other  outward  in  the  nerve  trunk 
into  the  body,  finally  ending  in 
some  sensitive  part,  e.g.  the  skin; 
Fig.  163.  If  the  skin  is  touched 
in  any  way  at  that  point,  an 
impulse  will  start  and  go  rapidly 
inv/ard  on  the  fibre,  pass  the 
neuron  cell  body  in  the  ganglion 
and  continue  into  the  cord.  In 
the  cord,  as  shown  also  in  Figure 
164,  the  fibre  again  divides,  one 
fibre  going  upward  and  the  other 
downward.  The  branch  passing 
up  the  cord  soon  divides  into  a 
number  of  twigs,  forming  at  c 
a  brush  of  fibrils  called  arboriza- 
tions. Close  to  these  arborizations 
begin  similar  divisions  of  another 
fibre  whose  cell  body  is  higher  up,  possibly  in  the  brain  itself: 
Fig.  164d      The  imDulse  which  enters  the  cord  mav  thus 


Fig.  163. — Diagram  illustrat- 
ing A  SIMPLE  REFLEX  ACTION 
The  impulse  from  the  sense  organ 
oasses  in  over  the  nerve  fibre,  a, 
and  may  pass  up  to  the  brain  over 
a-c.  But  a  part  may  be  switched 
off  through  e  down  the  fibre  /  to 
the  muscle,  causing  it  to  contra-ct 
without  the  aid  of  the  brain. 


312 


ADVANCED  PHYSIOLOGY 


jump  from  one  of  these  fibres  to  the  other  through  their 

tuft-like  endings  and  then  go  to  the  brain. 

But  there  is  another  direction  which  the  impulse  from  the 

skin  may  take  after  its  arrival  in 
the  cord.  The  branch  in  the 
cord  marked  a  in  Figure  164  also 
has  side  branches  ending  in  arbo- 
rations  e.  If  the  ingoing  impulse 
passes  out  into  these,  it  may  jump 
across  into  the  fibrils  of  another 
neuron  whose  fibre,/,  does  not  lead 
to  the  brain  at  all,  but  passes  out 
through  the  anterior  motor  root 
of  the  spinal  nerve  to  some  muscle. 
The  result  will  be  movement  at 
the  end  of  the  motor  fibres.  From 
the  course  which  the  impulse  in 
this  last  instance  took,  it  is  evi- 
dent that  the  resulting  motion 
must  have  occurred  without  the 
mediation  of  any  conscious  centers 
in  the  brain,  since  only  the  cells  of 
the  gray  matter  of  the  spinal  cord 
were  concerned  in  the  process. 
This  production  of  movement  in 
a  muscle  without  the  ''consent" 
of  any  conscious  centers  of  the 
brain  is  called  a  reflex  action.  In- 
voluntary movements  of  both  vol- 
untary and  involuntary  muscles 
occur  very  frequently  in  the  body 

and  play  an  important  part  in  life  processes.     They  will  be 

considered  at  greater  length  a  little  later. 

From  an  examination  of  Figure  164  it  is  easy  to  see  that 

two  results  might  follow  the  arrival  in  the  cord  of  an  impulse 


Fig.   164. — Diagram 
Illustrating  the  course  of  messages 
to  and  from    the    brain    through 
the  spinal  cord. 


{ 


NERVE  IMPULSES  AND  REFLEX  ACTION     -  313 

from  the  skin:  a  part  of  the  impulse  might  go  into  the  side 
branch,  e,  and  give  rise  to  a  reflex  movement,  while  the  rest  of 
the  impulse  could  take  the  path,  a,  leading  to  the  brain  and 
there  produce  sensation.  Influenced  by  this  sensation,  the 
brain  might  send  down  a  message  through  the  fibre,  g,  which 
would  result  in  conscious  movement,  in  addition  to  the  re- 
flex response.  Suppose,  for  example,  a  barefooted  boy  steps 
on  a  thistle.  He  jumps  off  quickly  (a  reflex  action).  In 
a  fraction  of  a  second  he  feels  the  prick  and  acts  accordingly, 
but  he  jumped  before  he  was  conscious  of  the  pain. 

The  neurons  described  are  those  in  the  spinal  cord  and 
spinal  ganglia,  but  there  are  a  large  number  in  the  brain  it- 
self. The  details  of  their  structure  are  slightly  different,  but 
their  general  relation  and  method  of  working  is  the  same. 

Outgoing  Paths. — Although  the  gray  and  white  materials 
of  the  brain  cortex  have  been  previously  referred  to  merely 
as  cells  and  fibres  respectively,  it  is  necessary  to  realize  that 
the  brain  material  is  a  mass  of  neurons  and  that  the  whole 
nervous  system  is  made  up  of  these  same  units.  The  white 
material  is  not  independent  of  the  gray ;  it  merely  consists  of 
the  axis  cylinder  fibres  of  the  neuron  cell  bodies  of  the  gray 
matter. 

The  cell  bodies  of  these  brain  neurons  receive  all  messages 
brought  to  them,  and  are  the  centers  of  the  thinking  pro- 
cesses. Decisions  are  made  in  them  and  they  start  impulses 
outward  to  any  part  of  the  body  which  they  have  decided  to 
move  or  influence.  These  impulses  pass  directly  downward 
over  an  axis  cylinder  (Fig.  164  g)  or  nerve  fibre,  which  finally 
ends  somewhere  in  the  cord  in  a  bimch  of  arborizations,  like 
those  already  described;  Fig.  164  h.  Very  near  these  fine 
endings  are  the  dendrites  of  another  neuron  body,  i,  and  into 
these  the  descending  impulses  pass.  The  long  axis  cylinder 
of  this  last  neuron  (Fig.  164  /)  passes  out  through  the  anterior 
or  ventral  root  of  a  spinal  nerve,  and  extends  directly,  with 
no  further  interruptions  or  * 'relay  neurons",  to  the  special 


314  ADVANCED  PHYSIOLOGY 

organ  which  it  is  to  supply.  In  this  way,  impulses  started 
by  the  brain  neurons  eventually  reach  the  muscles  to  be 
moved  or  the  tissue  to  be  innervated. 

REFLEX  ACTIONS 

We  have  already  noted  that  a  message  coming  into  the  cord 
from  the  body  may,  on  occasion,  be  switched  off  onto  side 
branches  of  the  fibre  it  was  traversing,  jump  from  its  terminal 
arborations  to  the  dendrites  of  a  neighboring  neuron,  and  go 
outward  over  the  anterior  root  of  a  spinal  nerve  without 
immediately  going  to  the  brain.  There  are  some  further 
aspects  of  these  reflex  actions  which  should  be  noted,  for  an 
almost  infinite  number  of  movements  and  minor  functions 
of  the  body,  as  well  as  many  very  important  ones,  are  thus 
performed. 

Probably  every  person  makes  more  movements  uncon- 
sciously than  consciously.  If  his  attention  were  especially 
called  to  each  one  of  his  actions,  they  would  immediately 
become  matters  of  all-absorbing  concern  to  him,  and  would 
take  so  much  of  his  time  that  he  would  be  able  to  attend  to 
nothing  but  the  simplest  activities.  Suppose,  for  example, 
that  one  had  to  think  definitely  about  the  contraction  of  each 
muscle  concerned  in  walking,  whenever  he  took  a  step;  sup- 
pose he  had  to  deliberate  about  the  contraction  of  every 
muscle  concerned  in  winking  every  time  he  moved  his  eyelids; 
suppose  that  every  time  his  clothing  touched  him  at  any 
point,  a  message  were  sent  to  his  centre  of  consciousness  in 
the  brain.  The  nervous  energy  required  would  be  almost 
incalculable,  and  the  maintenance  and  regulation  of  life 
would  be  impossible. 

We  have  already  found  that  the  essential  peculiarity  of  a 
reflex  movement  is  that  it  is  performed  without  the  media- 
tion of  any  of  the  conscious  centers  of  the  brain.  These  re- 
sponses can  indeed  be  obtained  in  animals  from  which  the 


NERVE  IMPULSES  AND  REFLEX  ACTION  315 

brain  has  been  entirely  removed.  The  fact  that  the  brain  of 
a  frog  can  be  taken  out,  and  yet  the  tissues  of  the  body  remain 
alive  for  a  considerable  time  (even  the  heart  may  go  on  beat- 
ing) makes  the  frog  an  especially  favorable  animal  for  this 
study.  Of  course,  such  a  frog  has  no  sensations  and  no 
ability  to  make  voluntary  motions,  still  it  shows  some  most 
interesting  reactions.  If  its  toe  be  pinched,  it  is  pulled  away 
quickly;  if  the  tip  of  the  toe  be  dipped  in  acid,  it  will  be  pulled 
out  promptly.  The  frog  acts  as  though  it  had  sensations  of 
pain,  though,  with  the  brain  wanting,  we  know  that  it  can 
have  none.  It  moves  because  the  impulses  excited  in  its 
nerve  endings,  after  reaching  the  cord,  cannot  go  to  the  brain, 
and  therefore  take  one  of  the  side  tracks  leading  across  arbora- 
tions  to  other  neuron  bodies,  whose  axis  cylinders  pass  im- 
mediately out  to  muscles  in  the  part  of  the  body  whence  the 
incoming  impulse  started. 

If  the  frog  has  its  brain,  a  different  result  may  follow,  for 
the  conscious  centers  will  become  aware  of  the  pinch  in 
the  toe  and  the  animal  may  decide  to  jump,  instead  of  simply 
pulling  its  foot  away.  In  this  case,  the  stimulus  has  of  course 
gone  all  the  way  to  the  brain  and  back  down  again,  finally 
passing  into  the  motor  cells  of  the  cord,  fibres  of  which  extend 
to  the  jumping  muscles.  Thus  we  see  that  the  same  muscles 
are  under  the  control  of  two  different  centers,  the  conscious 
center  of  the  brain  and  one  in  some  other  part  of  the  central 
nervous  system,  probably  in  the  cord  (as  we  have  assumed 
in  the  foregoing  instances).  Save  that  reflexes  are  usually 
quicker,  there  is  no  appreciable  difference  between  reflex  and 
conscious  movements. 

Reflex  movements  msLj  involve  the  brain,  as  well  as  the 
cord.  This  would  seem  an  impossibility;  i.  e.  the  unconscious 
action  of  a  conscious  center.  We  get  this  impression,  however, 
merely  because  as  a  rule  the  brain  is  thought  of  as  an  organ 
in  which  only  conscious  activity  occurs.  This  is  a  mistake,  for 
not  all  the  cells  of  the  brain  are  by  any  means  conscious  ce^ters. 


316  ADVANCED  PHYSIOLOGY 

It  is  not  difficult  to  cite  instances  of  brain  reflexes.  If  a 
sudden  light  flashes  in  front  of  the  eyes,  or  if  another  person 
shakes  a  handkerchief  or  other  solid  object  toward  the  face, 
one  shuts  the  eyes  instantly.  Now  a  person  does  not  stop 
to  think  whether  or  not  he  will  shut  his  eyes  under  these  cir- 
cumstances. They  are  closed  before  he  realizes  it  and  he 
himself  is  opening  them  carefully,  lest  the  danger  is  not  yet 
passed.  Yet  all  the  nerves  controlling  the  eye  muscles  come 
directly  from  the  brain,  and  the  centers  from  which  they 
arise  have  acted  without  the  person's  conscious  vohtion. 
Ordinary  winking  is  carried  on  unconsciously,  as  we  know. 
The  surface  of  the  eye  becomes  sUghtly  dry,  and  this  condi- 
tion irritates  it.  Messages  go  to  the  centers  controUing  the 
winking  muscles,  they  act  and  the  eyes  wink,  but  the  whole 
process  takes  place  without  one's  being  aware  of  it.  In  tak- 
ing food  into  the  mouth,  the  movements  of  the  tongue  and 
jaw,  while  under  one's  control,  nevertheless  occur  without 
conscious  thought  about  it.  One  does  not  say  to  himself, 
"I  will  now  shut  my  mouth,"  and  afterwards,  ''  I  will  now 
open  my  mouth."  These  are  only  two  of  the  innumerable 
instances  of  unconscious  action  on  the  part  of  brain 
centers. 

In  the  above  illustrations  of  reflex  actions  we  have  con- 
fined ourselves  to  visible  movements.  There  are  innumerable 
muscular  and  glandular  activities  in  the  body  of  which  one 
has  absolutely  no  intimation,  which  also  come  under  this 
head;  e.  g.  respiratory  movements  and  the  movements  of  the 
stomach  and  intestinal  walls.  Before  any  of  these  occur, 
messages  first  go  from  the  organ  concerned  to  the  central 
nervous  system.  For  example,  when  the  stomach  is  empty 
it  lies  perfectly  passive,  but  if  food  is  swallowed,  the  ends  of 
nerves  in  the  stomach  are  stimulated.  They  carry  the  mes- 
sage to  some  center  in  the  gray  matter  of  the  cord  or  brain,  or] 
both,  and  immediately  impulses  are  sent  out  over  motor  nerves 
to  the  muscles  of  the  stomach  walls,  which  then  begin  their! 


NERVE  IMPULSES  AND  REFLEX  ACTION  317 

churning  action.  In  the  same  way,  when  the  food  commences 
to  pass  on  into  the  intestine,  it  too  begins  its  complicated 
movements.  One  should  always  remember  that  these  occur 
only  because  certain  nerve  centers  are  acting. 

Reflex  Centers  as  Servants  of  Conscious  Centers. — It  is 
hardly  possible  to  overestimate  the  value  of  the  reflex  centers; 
it  is  only  through  them  that  the  conscious  centers  can  carry 
on  the  multitude  of  duties  which  devolve  upon  them.  One's 
attention  cannot  possibly  be  given  to  all  the  little  details  ot 
living,  so  these  are  turned  over  to  the  lower  parts  of  the  brain 
and  cord,  which  thus  act  as  a  great  coterie  of  servants.  To 
them  the  whole  control  of  many  activities  is  given  after  the 
decision  has  been  made  in  the  conscious  centers.  Take  the 
common  act  of  walking:  one  simply  directs  the  lower  center 
to  put  the  walking  muscles  into  proper  motion,  and  then  his 
attention  may  be  wholly  devoted  to  thinking  or  talking, 
while  the  reflex  center  will  superintend  the  walking  move- 
ments until  he  tells  it  to  stop. 

That  the  reflex  centers  are  servants  and  not  independent 
units  is  plain  when  we  notice  that  the  higher  centers  always 
keep  the  upper  hand,  so  to  speak.  With  adults,  walking  be- 
comes a  reflex.  Still,  by  an  interference,  the  conscious 
centers  can  interrupt  the  reflex  centers  at  any  time,  and  one 
can  stand  in  one  place  as  long  as  he  wishes,  starting  the  walk- 
ing reflex  again  when  he  chooses.  The  eyes  may  be  getting 
dry,  for  example,  and  the  tendency  of  the  neurons  in  reflex 
centers  is  to  make  the  winking  muscles  contract;  neverthe- 
less, by  giving  the  matter  conscious  thought,  one  can  inhibit 
the  winking  muscles  even  until  he  really  suffers  pain  in  the 
eyeballs.  One  can  also  stop  the  breathing  reflex  center  from 
acting  for  a  considerable  period.  Some  impulses  going  out 
from  the  brain  may,  therefore,  be  negative,  or  inhibitory  as 
we  say,  and  a  great  many  reflex  centers,  while  acting  with 
partial  independence  of  higher  control,  are  yet  constantly  liable 
to   its    dictates.      Others,    however,    like    the    involuntary 


318  ADVANCED  PHYSIOLOGY 

movements  of  internal  organs,  may  be  practically  beyond  any 
control  of  even  the  highest  centers. 

Relation  of  Reflex  Actions  to  Training  and  Habits. — The 
reflex  centers  in  all  cases  consist  of  the  nerve  cells,  the  central 
parts  of  some  of  the  neurons  or  of  groups  of  such  cells.  But 
the  interesting  and  important  fact  is  that  at  the  beginning  of 
one's  life  most  of  these  servants  are  untrained  and  cannot 
perform  at  all  the  duties  assigned  to  them  in  later  life.  Ex- 
actly how  these  nerve  centers  are  trained,  it  is  impossible  to 
say;  but  we  do  know  that  by  being  made  to  do  the  same  thing 
over  and  over  again  they  finally  learn  to  do  it  well,  and 
at  last  almost  without  one's  consciousness.  When  a  child 
first  learns  to  walk,  for  example,  his  muscles  do  not  readily 
work  out  his  will,  but  after  some  years  of  practice  he  no  longer 
thinks  of  the  motions,  for  the  reflex  centers  take  charge  of 
them.  Practice  makes  'perfect,  simply  because  by  constant 
use  the  reflex  centers  may  be  so  trained  that  they  do  their 
work  perfectly.  When  we  learned  to  write  we  were  obliged 
to  attend  carefully  to  the  motions  of  the  fingers,  to  see  that 
all  the  up-strokes  and  down-strokes  came  in  the  right  order. 
But  now,  if  we  are  good  writers,  we  do  not  have  to  think  of 
up-strokes  or  down-strokes,  hardly  of  the  letters.  We  think 
out  the  ideas  we  wish  to  put  on  the  paper,  and  reflex 
centers  take  charge  of  most  of  the  movements.  One 
becomes  aware  of  this  fact  when  he  tries  to  disguise  his  hand- 
writing. He  finds  such  a  procedure  as  difficult  as  he  did 
learning  to  write,  for  the  muscles  and  nerve  centers  are 
trained  to  do  a  thing  one  way,  and  continue  to  do  so. 

Most  of  the  activities  of  the  child's  life  have  for  their  pur- 
pose the  training  of  these  useful  nervous  centers.  His  work, 
his  play  and  his  study  all  have  the  same  end  in  view;  i.  e. 
training  for  his  use  a  set  of  faithful  servants  who  will  con- 
tinue for  the  rest  of  his  life  to  work  in  just  the  way  they  have 
been  taught  in  youth.  The  saying,  ''It  is  hard  to  teach  an 
old  dog  new  tricks,"  merely  expresses  the  difficulty  of  training 


NERVE  IMPULSES  AND  REFLEX  ACTION  316 

these  nerve  centers  in  any  new  way  after  a  person  has  grown 
up.  Education  of  the  body  and  the  mind  is  thus  first  of  all 
the  training  of  reflexes.  Since  one  must  employ  these  ser- 
vants all  the  rest  of  his  life,  it  is  of  the  greatest  importance 
that  they  be  trained  aright.  This  is  the  reason  why  it  is 
necessary  to  give  so  much  attention  to  education,  to  physical 
training  and  to  all  discipline  that  develops  useful  habits  of 
thought  or  action. 

THE  NERVE  IMPULSE 

We  have  mentioned  the  fact  that  nerve  impulses  pass  over 
the  nerve  fibres,  and  considering  the  differences  in  the  re- 
sults they  produce,  one  would  naturally  suppose  that  there 
would  be  corresponding  differences  in  the  impulses;  e.  g.  that 
the  impulse  which  produces  a  sensation  of  light  must  be  very 
different  from  one  producing  a  sensation  of  sound.  This  is 
not  the  case,  however.  An  electric  current  through  a  wire 
may  produce  different  results  according  to  the  different  kinds 
of  apparatus  employed  at  the  end  of  the  wire:  it  may  ring  a 
bell,  or  produce  light  in  a  bulb,  or  sound  in  a  telephone;  but 
though  the  results  are  various,  the  electric  current  is  essen- 
tially the  same  in  all  cases.  So  in  the  body,  the  impulse 
which  travels  over  a  nerve  is  always  essentially  the  same. 

No  one  need  be  told  that  nerve  messages  travel  over  the 
nerves  very  rapidly.  One  can  appreciate  no  lapse  of  time 
between  willing  to  move  the  fingers  and  their  actual  motion, 
and  yet  the  message  must  meantime  have  passed  from  the 
brain  to  the  muscles  concerned.  The  rate  at  which  messages 
pass  into  the  central  nervous  system,  i.  e.  the  rate  over  sen- 
sory nerves,  is  greater  than  that  at  which  messages  pass  out 
over  motor  nerves.  The  former  travel  inward  about  140 
feet  per  second,  while  the  latter  travel  outward  at  a  rate  of 
about  110  feet  per  second. 

But  what  is  the  impulse  which  travels  over  nerves?  The 
old  idea  was  that  the  nerves  were  hollow  and  filled  with  a 


320  ADVANCED  PHYSIOLOGi: 

fluid,  but  we  know  now  that  this  is  false.  Among  other 
ideas  which  have  been  held  concerning  this  question  are  the 
following: 

1.  The  chemical  theory  maintains  that  when  a  nerve  is 
stimulated,  a  chemical  disturbance  passes  along  the  axis  cylin- 
der of  the  neuron  involved.  This  may  be  compared  to  the 
change  which  takes  place  in  a  tiny  trail  of  gunpowder  when 
one  end  of  the  line  is  ignited.  The  difficulty  in  accepting 
this  theory  is  that  we  should  have  to  imagine  the  train  of 
material  in  a  nerve  to  be  instantaneously  replaced,  so  that 
the  nerve  would  be  ready  to  transmit  another  message  at 
once. 

2.  The  mechanical  theory  assumes  that  the  molecules 
of  the  nerve  fibres  are  in  close  contact,  and  that  any 
unusual  movement  of  them  at  one  end  of  a  nerve  is 
transmitted  through  the  whole  line  until  it  is  felt  at  the 
other  end.  Suppose  the  molecules  are  compared  to  croquet 
balls  placed  in  contact,  in  a  long,  straight  line.  If  one  at 
the  end  is  struck  the  one  at  the  opposite  end  bounds  away 
from  the  others,  though  the  intervening  balls  do  not  move 
appreciably. 

3.  The  electrical  theory  looks  upon  the  nerve  impulse  as 
an  electrical  phenomenon.  It  can  easily  be  excited  by  an 
electric  shock,  it  travels  very  rapidly  over  the  nerve  without 
seeming  to  produce  any  changes  in  it,  and  in  these  respects 
resembles  electricity.  Then,  too,  careful  study  shows  that 
there  are  electric  changes  in  the  nerve  when  the  impulse 
passes  over  it.  Sometimes  an  impulse  is  supposed  to  jump 
from  one  fibre  to  another  as  an  electric  current  may  jump 
from  one  wire  to  another.  On  the  other  hand,  the  nerve 
impulse  differs  from  electricity  in  several  important  respects. 
It  travels  too  slowly,  100  feet  per  second  being  too  slow  for 
electricity.  If  a  string  is  tied  tightly  around  a  nerve  it  will 
stop  the  passage  of  the  nerve  impulse,  but  such  treatment  of 
an  electric  wire  will  not  stop  an  electric  current  over  it.     If 


NERVE  IMPULSES  AND  REFLEX  ACTION  321 

a  nerve  is  cut  and  the  ends  put  together  ever  so  carefully,  still 
no  impulse  will  pass  over  the  break.  Cutting  electric  wires 
in  no  way  impairs  them;  even  though  the  ends  be  put  to- 
gether carelessly  the  current  will  pass  along  perfectly,  if  only 
there  is  good  contact.  Lastly,  the  nerve  fibre  is  a  poor 
conductor  of  electricity. 

Taking  all  these  facts  together,  it  would  seem  that  the 
nerve  impulse  is  not  exactly  Uke  any  other  kind  of  force  with 
which  we  are  acquainted.  Although  it  certainly  resembles 
electricity  in  many  respects,  at  present  it  is  regarded  as  a 
special  kind  of  impulse  that  travels  rapidly  through  the  nerve 
fibre  from  any  point  where  it  may  be  started  to  the  other 
end. 

Nerve  impulses  may  be  instituted  by  many  different 
methods.  In  the  body  they  usually  start  from  some  part  of  a 
neuron,  but  we  do  not  yet  know  the  method  by  which  this 
is  brought  about.  Impulses  may  also  be  started  artificially. 
If  an  electric  shock  is  sent  into  a  nerve,  an  impulse  is  excited 
and  travels  to  the  nerve  ending;  if  the  nerve  is  pinched  or  cut, 
an  impulse  starts  from  the  point  of  injury.  If  a  hot  body 
touches  the  nerve,  or  certain  chemicals  are  dropped  upon  it, 
these  will  also  give  rise  to  a  nerve  impulse.  In  some  nerves 
an  impulse  is  started  by  light,  in  others  by  sound  etc. 

CARE  OF  THE  BRAIN 

Under  the  conditions  of  modern  life  to  a  far  greater  extent 
than  in  earlier  centuries  it  has  become  necessary  for  each  in- 
dividual to  use  his  brain.  While  some  occupations  require 
this  more  than  others,  there  is  none  in  which  one  is  not  helped 
in  the  achievement  of  success  by  having  a  well-trained  and 
active  brain.  Education  gives  this  training.  As  the  years 
of  school  life  pass,  the  brain  not  only  obtains  information, 
but  it  learns  how  to  act;  it  grows  stronger  by  use  just  as 
muscles  do. 

We  sometimes  hear  of  persons  whose  health  has  broken 


322  ADVANCED  PHYSIOLOGY 

down  because  of  excessive  mental  work  resulting  in  nervous 
strain.  Since  such  a  condition  is  very  unfortunate  and  very 
serious,  it  is  important  to  learn  what  causes  contribute  to  it. 

In  the  first  place  we  may  be  confident  that  only  in  very 
rare  cases  is  the  trouble  due  to  overwork,  or  to  excessive  study. 
The  brain  gains  strength  by  use,  and  even  a  very  hard  student 
is  not  likely  to  use  it  too  severely,  if  he  is  otherwise  in  proper 
health.  If  the  brain  is  treated  reasonably,  and  the  whole 
body  kept  in  a  state  of  health,  the  brain  may  work  very 
hard  and  grow  stronger  all  the  time.  But  the  person  who  is 
fond  of  study  is  apt  to  neglect  entirely  the  other  functions  of 
his  body,  and  allow  his  muscles  and  other  organs  to  lack 
proper  exercise.  Exercise,  especially  in  fresh  air  to  produce 
vigorous  respiration,  helps  to  keep  the  brain  alert.  The 
student  perhaps  fails  to  use  proper  discretion  in  his  diet; 
overeating,  irregular  eating  and  too  rich  foods  throw  his 
body  out  of  condition.  The  brain  needs  good  wholesome 
food  to  keep  it  active,  and  it  is  well  to  remember  that  there 
are  no  special  "  brain  foods,"  this  term  being  used  simply  to 
catch  trade  for  certain  food  products.  The  student  neglecting 
some  of  these  plain  laws  of  health,  becomes  ill  and  his  break- 
down is  apt  to  be  considered  due  to  over-study. 

It  is  working  the  brain  under  improper  conditions  rather 
than  working  it  too  hard  that  produces  nerve  strain.  Using 
the  brain  excessively  without  sufficient  outdoor  exercise, 
studying  late  at  night  when  one  needs  sleep,  using  it  too  long 
upon  the  same  kind  of  work,  are  all  likely  to  injure  it.  Rest 
and  sleep  are  necessary  for  an  active  brain.  The  amount  of 
sleep  needed  is  not  the  same  for  all  persons,  and  growing^ 
people  require  more  than  adults.  In  general  about  eight| 
hours  sleep  in  a  day  should  be  taken  by  every  one,  and  more 
than  this  by  children.  The  attempt  to  study  after  one  has 
become  sleepy  is  always  a  mistake;  in  the  first  place  it  is  the 
hardest  tax  on  the  brain,  and  in  the  second  place  it  is  often 
useless.     The  brain  is  not  in  condition  to  receive  and  remem- 


NERVE  IMPULSES  AND  REFLEX  ACITON  323 

ber,  and  it  will  be  found  the  next  day  that  almost  nothing  is 
retained  of  that  which  was  studied  the  night  before,  so  that 
the  hard  work  was  of  no  value.  The  bad  habit  of  cramming 
should  be  particularly  avoided.  To  accomplish  the  most  in 
the  way  of  learning,  one  should  do  a  proper  amount  of  work 
regularly  each  day.  If  this  is  done,  it  will  be  found  that 
when  the  time  comes  for  examinations,  cramming  will  not  be 
necessary.  The  poorest  way  to  prepare  for  an  examination 
is  to  sit  up  late  the  night  before,  vainly  trying  to  crowd  into  a 
tired  brain  the  information  which  should  have  been  previously 
acquired.  Too  long  continued  attention  given  to  one  sub- 
ject is  also  a  mistake.  A  change  of  occupation  is  sometimes 
just  as  much  of  a  rest  as  to  stop  work  entirely.  To  work 
with  the  muscles  is  a  rest  from  study,  and  reading  is  a  rest 
from  muscular  work;  to  study  algebra  is  also  a  rest  from  the 
study  of  language,  although  both  of  these  require  brain 
work. 

The  condition  of  the  body  is  largely  modified  by  the  con- 
dition of  the  mind.  We  know,  for  example,  that  one's 
emotions  affect  the  beating  of  the  heart.  Worry  and  anxiety 
are  matters  which  have  their  origin  in  the  mind;  but  their 
actual  effect  may  take  very  unfortunate  forms;  e.  g.  loss  of 
appetite,  inability  to  sleep,  super-sensitiveness,  lack  of  in- 
terest in  things  in  general.  These  and  many  other  of  our  little 
ills  are  made  worse  by  continually  thinking  of  them.  On 
the  other  hand,  health  is  augmented  by  cheerfulness  and 
mental  buoyancy.  Muscular  fatigue,  or  even  headache  and 
toothache  often  disappear  before  a  game  of  tennis  or  baseball, 
or  during  an  evening  of  music.  Digestive  juices  are  more 
readily  secreted  when  one  is  in  good  spirits,  than  when  one 
is  nervous  or  worrying.  All  of  these  things  show  that  the 
mind  has  a  decided  effect  upon  the  condition  and  general 
health  of  the  body, — a  fact  which  imposes  upon  one  the 
possibility  and  duty  of  cheerfulness,  not  only  because  of  the 
advantage  to  himself  but  for  the  sake  of  others. 


324  ADVANCED  PHYSIOLOGY 


SYMPATHETIC  SYSTEM  OF  NERVES 

The  term  sympathetic  system  has  been  applied  to  a  series 
of  nerve  cells  and  fibres  which  connect  all  the  spinal 
nerves  and,  to  a  certain  extent,  bind  them  together, 
not  only  anatomically,  but  to  a  limited  extent  in  their 
functional  work  also.  Just  how  far  there  is  any  co- 
operation of  this  kind  is  uncertain,  and  the  term  ''sym- 
pathetic," is  not  well  applied. 

This  system  comprises  two  strands  of  nerve  tissue  lying  in 
the  body  cavity,  one  on  each  side  of  the  back  bone;  Fig.  153. 
Each  line  of  fibres  makes  connections  with  each  of  the  spinal 
nerves  on  its  side  of  the  body,  and  at  the  junction  with  each 
spinal  nerve  a  ganglionic  collection  of  nerve  cells  is  formed. 
Of  course,  no  impulses  really  originate  in  the  cords  of  the 
sympathetic  system,  but  the  fibres  in  them  take  up  impulses 
which  have  come  out  over  spinal  nerves,  from  the  spinal  cord 
or  from  the  brain. 

The  majority  of  branches  from  the  sympathetic  system  go 
to  the  blood  vessels  in  the  abdominal  region,  and  exercise  con- 
strictor effects  on  them.  Some  go  to  the  heart,  others  branch 
and  make  an  extensive  network  of  fibres  which  here  and 
there  fuse  together  forming,  with  the  addition  of  nerve  cells, 
ganglia.  Such  ganglia  are  seen  in  the  walls  of  the  stomach, 
in  the  body  cavity,  in  the  "  small  of  the  back  "  and  also  in 
the  neck,  and  from  these  ganglia,  nerves  pass  out  to  near-by 
organs.  The  secretion  of  some  of  the  large  glands  like  the 
liver  is  controlled  by  impulses  reaching  them  over  the  sym- 
pathetic fibres.  As  a  rule,  the  impulses  which  pass  through 
the  sympathetic  system  are  not  under  the  control  of  the  will, 
and  furthermore  they  generally  provoke  responses  from  the 
organ  to  which  they  go  of  the  very  opposite  character  to  that 
produced  by  impulses  over  the  ordinary  spinal  or  cranial 
nerves.  For  instance,  the  sympathetic  nerves  going  to  the 
laeart  carry  messages  that  stimulate  it  to  more  rapid  action. 


^'  NERVE  IMPULSES  AND  REFLEX  ACTION  325 

while  those  going  over  the  vagus  nerves,  direct  from  the  brain, 
produce  a  slowing  effect. 

DISEASES  OF  THE  NERVOUS  SYSTEM 

If  there  is  trouble  in  the  brain  it  is  liable  to  affect  the  whole 
life  of  the  individual  and  especially  his  intelligence. 

Idiocy. — Sometimes  a  person  is  born  with  the  brain  only 
partially  developed,  and  even  as  he  grows,  it  never  becomes 
as  large  as  it  should.  The  skull,  too,  is  usually  small  and 
peculiarly  shaped.  With  an  abnormally  small  brain  there 
is  sure  to  be  found  imperfect  intelligence,  and  such  a  person 
is  called  an  idiot.  Idiocy  is  thus  a  lack  of  normal  intelligence, 
due  usually  to  the  failure  of  the  brain  to  reach  its  full  size. 
Size  alone  may  not  determine  the  degree  of  intelligence  in  an 
individual.  Frequently  abnormal  conditions  in  other  organs 
(especially  the  thyroid)  may  produce  defective  mentality. 

Insanity. — On  the  other  hand,  a  person  may  have  a  well 
developed  brain,  but  something  may  occur  to  interfere  with 
its  proper  functioning.  Sometimes,  for  example,  an  abscess 
grows  inside  the  skull  and  presses  on  the  brain;  or  after  cer- 
tain accidents,  a  bit  of  bone  may  press  in  upon  it.  In  all  such 
cases  the  mental  powers  of  the  person  are  thrown  out  of 
balance;  he  may  imagine  all  sorts  of  strange  things,  e.g.  that 
he  is  another  person,  or  he  may  become  violent  and  dangerous. 
Indeed,  it  is  never  possible  to  tell  what  he  may  do  or  think, 
and  we  call  a  person  whose  mind  is  so  affected,  insane.  In- 
sanity is  very  different  from  idiocy,  for  it  is  due  to  the  de- 
rangement of  brain  functions  which  were  originally  normal. 
Insanity  varies  from  a  very  mild  type  in  which  the  person  is 
perfectly  sane  on  alinost  all  subjects,  but  cannot  think  clearly 
on  some  one  topic,  to  that  in  which  the  person  is  violent,  and 
his  thinking  powers  are  completely  upset. 

Inasmuch  as  insanity  is  due,  sometimes,  to  some  pressure 
on  the  brain,  it  is  occasionally  possible  to  cure  it  by  a  surgical 
operation;  in  many  cases,  however,  there  is  no  cure.     When  a 


§26  ADVANCED  PHYSIOLOGY 

person  is  born  with  the  skull  or  some  other  part  so  improperly 
shaped,  that  the  brain  does  not  have  the  chance  to  develop 
rightly,  a  pecuHar  disposition  may  result.  The  person  may 
be  excessively  irritable,  he  may  be  subject  to  fits,  or  quite 
lacking  in  any  ideas  of  right  and  wrong,  and  thus  apt  to  be- 
come a  criminal.  In  some  instances  a  slight  operation  has 
completely  relieved  these  conditions,  and  a  decided  change 
in  the  person  been  produced. 

Paralysis,  or  Shock. — The  breaking  of  a  blood  vessel  is  one 
of  the  most  serious  accidents  which  may  occur  in  the  nervous 
system.  It  rarely  happens  in  young  people,  although  it 
occurs  frequently  in  older  ones.  The  breaking  of  a  vessel 
usually  produces  a  clot  which  may  then  press  upon  nerves 
and  cause  the  trouble  commonly  called  nervous  shock.  The 
kind  of  trouble  produced,  however,  varies  with  the  location 
of  the  clot.  If  this  should  be  in  the  spinal  cord,  it  may  more 
or  less  completely  cut  off  communication  between  the  brain 
and  the  parts  of  the  body  below  it.  This  of  course  would 
mean  that  both  sensation  and  power  of  movement  might  be 
lost  in  these  lower  organs,  i.e.  the  person  would  be  paralyzed. 
If  the  clot  is  in  the  brain,  and  that  organ  is  hindered  in  its 
functions,  this  also  may  produce  paralysis.  In  sensory 
paralysis,  only  sensations  are  lost,  the  person  can  move  the 
body  but  cannot  feel;  in  motor  paralysis  he  retains  the  power 
of  sensation,  but  cannot  move;  in  complete  paralysis,  both  1 
movement  and  sensation  are  wanting. 

Recovery  from  this  trouble  is  not  very  common.     If  it  is 
due  to  a  broken  blood  vessel  and  the  clot  is  not  too  large,  itj 
may  be  dissolved  and  more  or  less  completely  disappear.     If 
it  is  on  the  surface  of  the  brain  it  may  be  removed  by  a  surgi- 
cal operation,  but  another  break  of  the  same  kind  is  always] 
apt   to   occur.     Paralysis   is   an   indication   of   the   weaken-] 
ing   of  bodily  vigor,    and   usually    a    sign    of    approaching 
old  age. 

XTervous  Prostration. — Nervous  prostration  is  the  common] 


NERVE  IMPULSES  AND  REFLEX  ACTION  327 

name  for  an  affection  of  the  nervous  system,  concerning 
the  cause  of  which  httle  is  known.  It  sometimes  occurs 
when  one  has  been  living  for  a  long  time  under  great  nervous 
tension,  such  as  comes  from  continued  excitement,  too  little 
sleep  or  constant  anxiety.  It  occurs  more  frequently  in 
civilized  life  and  the  highly  complex  conditions  of  modern 
society  than  in  the  simpler  life  of  the  country.  The  symp- 
toms of  this  trouble  are  too  varied  to  be  described  here,  but 
very  often  the  person  imagines  himself  ill  from  troubles  which 
do  not  exist,  and  is  in  a  constant  state  of  worry  about  his  own 
health.  The  remedy  for  nervous  prostration  is  a  complete 
change  of  life  to  relieve  the  body  from  the  kind  of  strains 
which  have  been  producing  t^e  trouble.  If  one  lives  simply, 
takes  life  as  calmly  as  possible,  does  not  allow  himself  to 
worry  nor  live  too  highly,  he  is  well  protected  against  this 
illness.  Nervous  prostration  does  not  usually  result  from 
overwork,  as  has  been  frequently  supposed.  It  is  more 
likely  to  follow  wrong  habits  as  regards  food,  sleep,  recreation 
etc.  If  one  breaks  the  monotony  of  work  occasionally  with 
a  brief  period  of  real  recreation,  he  may  work  very  hard  and 
long  without  serious  consequences. 

Cerebro-spinal  Meningitis. — Meningitis  is  one  of  the  very 
serious  diseases,  frequently  fatal,  and  is  caused  by  a  certain 
bacterium  which  attacks  the  brain.  It  is  more  common 
among  children  than  adults  and  sometimes  occurs  in  epidemics. 
Its  method  of  passing  from  individual  to  individual  is  not 
known,  nor  its  means  of  entering  the  body.  It  is  certainly 
not  very  contagious,  rarely  more  than  one  case  occurring  in  a 
family.  Our  lack  of  knowledge  as  to  its  method  of  distribu- 
tion has  prevented  the  devising  of  efficient  rules  for  avoiding 
it,  and  the  only  suggestions  now  possible  are  to  keep  up  the 
general  health  and  to  avoid  contact  with  those  suffering  from 
the  disease,  and  with  secretions  from  their  mouths.  A  method 
of  combatting  it  by  inoculation  has  been  devised  that  is  fre- 
quently successful  in  producing  a  cure. 


CHAPTER  XX* 
A  CLEAR  MIND  THE  NEED  OF  THE  DAY 

Every  living  being  must  contend  with  enemies  for  its  own 
existence.  In  the  early  periods  man  counted  among  his  foes 
wild  animals,  storms,  floods,  famines  and  droughts.  Against 
these  he  has  in  a  large  measure  ceased  to  contend;  he  has 
overcome  wild  animals,  and  with  fires,  houses  and  various 
other  devices  can  defend  himself  against  the  elements  of 
nature.  It  is  due  to  the  wonderful  power  of  his  mind  that  he 
has  been  able  to  master  these  enemies,  and  it  certainly  be- 
hooves him  to  keep  this,  his  greatest  treasure,  in  as  efficient 
condition  as  possible. 

Man  is  still  engaged  in  a  struggle  for  existence  with  certain 
foes  which  his  changed  conditions  have  brought  prominently 
forward,  and  the  struggle  is  all  the  more  severe  because  he 
does  not  always  recognize  his  worst  foes  as  foes  at  all.  Among 
the  most  dangerous  of  his  remaining  enemies  is  the  micro- 
scopic, parasitic  germ.  Doubtless,  germs  existed  in  the  early 
periods  of  man's  existence,  but  they  were  not  especially 
serious  until  people  came  to  live  in  crowded  communities. 
The  larger  the  community  the  greater  becomes  the  danger 
from  microbes.  An  epidemic  may  kill  thousands  and  other 
diseases,  like  tuberculosis,  which  do  not  produce  violent 
epidemics,  are  quietly  at  work  destroying  the  lives  of  hundreds 
of  thousands  each  year.  Germs  are  particularly  dangerous 
because  they  are  invisible,  because  people  do  not  know  where 
they  are  nor  how  to  avoid  them,  and  because  they  are  capable 
of  multiplying  so  fast  that  no  matter  how  many  of  them  are 
destroyed,  their  numbers  can  in  a  few  days  be  fully  replaced 
^  This  chapter  is  entirely  the  work  of  the  senior  author. 
328 


A  CLEAR  MIND  THE  NEED  OF  THE  DAY  32& 

by  the  rapid  multiplication  of  those  which  remain.  Man  is, 
however,  learning  to  fight  them,  more  and  more  successfully. 
Microscopes  are  discovering  where  they  are,  and  careful 
scientific  studies  are  showing  how  in  a  measure  they  may  be 
avoided.  Indeed,  through  modern  sanitation,  which  has 
driven  them  backward  and  has  reduced  the  number  and 
violence  of  epidemics,  men  have  succeeded  in  making  the  city 
almost  as  secure  against  microbes  as  the  country.  We  shall 
notice  in  another  chapter  some  of  the  methods  adopted  today 
in  fighting  this  worst  enemy  in  our  struggle  for  existence. 

THE  USE  OF  DRUGS  THAT  AFFECT  THE  BRAIN 

Another  enemy  against  which  man  has  to  contend  is 
especially  dangerous  because  it  also  is  not  commonly  recog- 
nized as  a  foe.  Indeed,  many  people  look  upon  it  as  a  friend, 
while  others  regard  it  as  a  luxury,  which  may  be  indulged  in 
more  or  less  frequently  without  thought  of  danger.  The 
nervous  system  controls  the  whole  body,  and  everything  that 
affects  the  activities  of  the  brain  has  a  profound  influence  upon 
the  whole  life.  But  some  men  have  unfortunately  developed 
the  habit  of  using  certain  substances  which  have  a  direct 
action  on  that  organ  and  interfere  with  its  normal  functions. 
There  are  two  classes  of  brain  drugs:  stimulants,  and  nar- 
cotics— each  of  which  has  pernicious  effects. 

Stimulants. — There  is  great  difference  of  opinion  as  to  the 
proper  definition  of  the  word  stimulant.  This  term  usually, 
however,  denotes  a  drug  that  will  excite  an  organ  to  increased 
activity.  The  effect  is  temporary  and  does  not  indicate  in- 
creased strength,  but  only  enables  the  body  to  call  upon  its 
reserve  power  a  little  more  quickly.  In  most  cases,  if  not  in 
all,  the  stimulating  action  is  followed  by  a  corresponding 
depression  so  that  there  is  no  gain  in  the  end.  A  whip  gives 
no  power  to  a  jaded  horse,  though  it  may  excite  him  for  a 
short  time  to  more  exertion.  The  constant  use  of  a  stimu- 
lant, too,  acts  somewhat  like  the  constant  use  of  a  whip  on  a 


330  ADVANCED  PHYSIOLOGY 

horse;  the  animal  soon  ceases  to  mind  the  whip,  or  refuses  to 
go  without  its  constant  application.  The  only  substances  in 
common  use  which  act  in  this  way  are  coffee  and  tea  (caffein 
and  thein).  Persons  who  have  become  accustomed  to  these 
stimulants  are  no  longer  normal  individuals,  they  cannot 
readily  work  without  them  and  really  suffer  if  deprived  of 
them.  Sometimes  the  effect  of  tea  and  coffee  is  so  great  as 
to  cause  positive  ill  health. 

Strychnin,  which  is  a  deadly  poison  when  taken  in  con- 
siderable quantity,  will,  when  given  in  small  amounts,  quicken 
the  heart  beat.  For  this  reason  it  has  been  prescribed  by 
physicians  in  cases  of  critical  illness  where  it  is  necessary  to 
accelerate  the  action  of  the  heart,  and  it  has  therefore  been 
called  a  heart  stimulant.  The  habit  of  using  even  mild  stimu- 
lants like  tea  and  coffee  is,  however,  a  useless  and  very  un- 
wise one  for  young  people  to  acquire. 

Narcotics. — Narcotics  have  an  effect  the  reverse  of  that  of 
stimulants.  Instead  of  producing  an  increase  of  activity, 
they  lessen  it;  instead  of  making  the  organs  work  more  vigor- 
ously, they  dull  and  render  them  less  efficient.  In  particular 
they  have  the  effect  of  causing  the  brain  to  become  sluggish 
and  finally  of  putting  it  to  sleep.  Just  as  fast  as  the  brain 
comes  under  their  influence,  it  loses  its  unique  pov/ers.  The 
use  of  a  narcotic  thus  deprives  the  individual  of  his  most 
valuable  possession. 

The  commonest  narcotics  are  opiates;  e.g.  laudanum,  pare- 
goric, morphine,  soothing  syrup.  Cocaine,  chloral,  chloroform, 
ether  and  the  like  also  produce  a  deadening  effect,  though 
their  action  is  different  from  the  opium  products.  When 
one  of  these  drugs  has  an  action  on  the  brain  strong  enough 
to  cause  unconsciousness,  it  is  said  to  act  as  a  general  anes- 
thetic, and  if  it  produces  insensibility  to  pain  in  only  one 
particular  part  of  the  body  without  causing  unconsciousness,] 
it  is  called  a  local  anesthetic. 

Narcotics  have  their  useS;,  and  as  a  means  of  relieving  P^iil' 


A  CLEAR  MIND  THE  NEED  OF  THE  DAY  331 

in  emergencies  they  have  been  of  incalculable  benefit.  But 
most  of  them  have  an  unfortunate  tendency  to  create  an 
appetite,  before  which  in  the  end  the  user  becomes  helpless. 
A  person  begins  with  a  small  dose,  perhaps  at  the  advice  of  a 
physician  to  relieve  pain,  and  continues  to  repeat  it  either 
for  the  same  purpose  or  for  some  other  reason,  until  the  habit 
of  frequently  using  the  narcotic  is  formed.  The  small  doses 
cease  to  have  the  desired  effect,  the  more  it  is  used  the  more  it 
is  craved  and  the  larger  are  the  amounts  taken.  Surely  and 
even  rapidly  this  undermines  the  health  and  destroys  the  will 
power  until  the  man  becomes  a  wreck.  Usually  he  does  not 
appreciate  the  fact  that  he  is  coming  under  the  influence  of 
the  drug  until  he  becomes  its  slave,  and  when  he  does  recog- 
nize that  he  is  being  ruined  he  is  usually  too  far  gone  to  wish 
to  reform,  or  his  will  power  is  too  much  shattered  to  enable 
him  to  do  so. 

There  are  few  more  difficult  habits  to  conquer  than  the 
opium  habit  and  the  only  safe  way  to  escape  this  great  danger 
is  by  avoiding  the  use  of  this  narcotic  entirely.  The  same 
applies  to  the  use  of  cocaine  and  chloral.  The  amount  of  in- 
jury done  to  children  by  the  ignorant  use  of  soothing  syrups 
by  their  mothers  or  nurses  cannot  be  calculated,  and  it  is 
doubtless  true  that  many  a  child's  death  is  due  to  the  use  of 
such  drugs,  most  of  which  contain  opium  or  a  similar  narcotic. 
One  should  hesitate  about  the  continued  use  of  any  drugs 
which  rapidly  relieve  pain  or  induce  sleep,  though  some  ere 
more   injurious   than   others. 

Alcohol. — The  most  commonly  used  drug  belonging  to  the 
class  of  narcotics  is  alcohol.  The  dispute  about  the  food  value 
of  alcohol  has  already  been  mentioned,  but  there  is  no  ques- 
tion about  classing  alcohol  as  a  drug  which  provokes  the 
brain  to  abnormal  action.  If  it  is  used  constantly  and  in 
large  amounts,  it  not  only  affects  the  brain  but  other  organs. 
An  inflammation  in  the  form  of  chronic  catarrh  is  produced 
ID  the  stomach,  and  the  functional  activities  of  that  organ  are 


332  ADVANCED  PHYSIOLOGY 

decidedly  impaired.  In  the  liver  a  peculiar  disease  called 
cirrhosis  sometimes  appears,  the  liver  becoming  hardened  and 
enlarged.  The  kidneys  become  enlarged  by  the  formation  of 
useless  connective  tissue  which  encroaches  upon  the  kidney 
proper  and  weakens  its  action.  The  heart  is  sometimes  en- 
larged and  weakened.  The  blood  vessels  are  permanently 
dilated,  producing  for  example,  the  red  nose  which  often 
marks  those  addicted  to  alcohol.  Accompanying  indulgence 
in  some  forms  of  alcoholic  drinks  there  is  a  tendency  to  the 
formation  of  an  abnormal  amount  of  fat,  which  is  only  an 
incumbrance  and  tends  to  interfere  with  the  normal  func- 
tioning of  certain  organs.  It  is  usually  deposited  in  the 
abdomen  but  may  be  stored  around  the  heart,  tending  to 
check  its  free  action  and  produce  heart  troubles.  All  of 
these  phenomena  are  abnormal,  and  indicate  that  alcohol 
deranges  the  body  functions.  Physicians  recognize  alcohol- 
ism as  a  very  real  and  very  serious  disease  brought  on  by  the 
use  of  alcoholic  drinks.  When  small  amounts  only  are  taken 
derangements  are  less  evident,  although  the  difference  is 
probably  in  degree  rather  than  in  kind. 

In  all  cases  alcohol  has  some  action  on  the  brain,  and  the 
nervous  system  as  a  whole  is  the  one  most  affected  by  it. 
Here  its  influence  seems  to  be  from  the  first  that  of  a  narcotic, 
since  it  always  tends  to  dull  the  brain  activities.  One  of  its 
first  effects  is  to  stupefy  the  vaso-motor  center.  We  have 
learned  that  this  center  governs  circulation  in  general,  al- 
ways acting  in  such  a  way  as  to  keep  the  small  arteries  parti v 
closed,  and  thus  regulating  the  amount  of  blood  sent  to  dif- 
ferent parts  of  the  body.  When  this  center  is  dulled  the 
small  arteries  relax  and  the  blood  rushes  through  them  faster 
than  usual,  the  cheeks  become  flushed  and  the  skin  warmed; 
thus  what  appears  to  be  an  increased  activity  is  really  an 
effect  of  the  narcotic  action  of  alcohol  on  the  brain.  This 
increase  of  blood  flow  also  affects  the  brain  itself,  causing  a 
feeling  of  excitement,  a  certain  hilarity  of  spirits  which  is 


A  CLEAR  MIND  THE  NEED  OF  THE  DAY  333 

commonly  mistaken  for  increased  mental  activity.  Hence 
the  stimulating  effect  oi  alcohol  is  only  apparent  and  is  really 
due  to  the  partial  paralyzing  of  the  vaso-motor  center. 

The  question  whether  alcohol  is  to  be  regarded  as  a  narcotic 
or  a  stimulant  has  been  very  much  debated,  due  partially  to 
the  difficulty  of  defining  the  word  stimulant,  and  partly  to 
the  pseudo-stimulating  action  of  alcohol.  It  is  certainly 
true  that  many  people  have  believed  and  still  believe  that  it 
"gives  strength."  Indeed  there  is  little  doubt  that  many 
persons  have  learned  to  use  it  under  a  genuine  conviction 
that  it  makes  them  stronger  and  even  that  it  makes  them 
think  more  quickly.  But  these  beliefs  are  wholly  unfounded. 
Alcohol  does  not  give  strength.  At  the  risk  of  direct  in- 
jury to  many  internal  organs,  it  will  furnish  an  extremely 
small  amount  of  heat,  although  sugar  and  fat  will  do  this 
much  better.  No  one  who  understands  the  facts  would  ever 
use  it  when  he  has  any  hard  work  to  do  under  the  impres- 
sion that  it  can  under  any  conditions  make  him  more  effi- 
cient. 

Effects  of  Alcohol  on  the  Brain. — The  most  noticeable  effect 
of  alcohol  is  that  upon  the  brain.     Its  use  is  followed  by  a 
feeling  of  excitement  and  flow  of  spirits  that  resembles  very 
much  the  result  of  a  stimulant.     But  this,  too,  is  really  due 
to  the  fact  that  its  narcotic  action  has  dulled  the  person's 
feeling  of  reserve  and  self  control.     He  is  apt  to  do  anything 
that  comes  into  his  mind  or  say  anything  that  impulse  sug- 
gests, whereas  ordinarily  he  would  think  further  before  speak- 
ing.    Hence  he  speaks  and  laughs  more  easily,  and  in  general 
acts  as  if  stimulated,  when  the  fact  is  that  he  has  merely  lost 
;     the  valuable  power  of  self  restraint.     The  man  who  keeps  his 
I     brain  clear  and  uninfluenced  by  alcohol  is  usually  more  than 
a  match  for  the  one  who  has  ^'stimulated"  his  mind  by  wine 
I     or  other  alcoholic  drink. 

The  action  of  alcohol  does  not  stop  here,  however.     From 
the  first  it  dulls  the  powers  of  perception  and  makes  one  less 

m 


334 


ADVANCED  PHYSIOLOGY 


quick  to  see  and  understand;  one  does  less  work  or  does  it  not 
so  well,  although  oddly  enough  he  thinks  that  he  is  doing  better 
than  usual.  If  more  than  a  very  small  quantity  of  alcohol  is 
used,  its  narcotic  action  becomes  extremely  apparent.  Even 
before  the  person  has  any  appreciation  of  the  fact  that  the 
alcohol  has  influenced  him  at  all,  it  has  begun  its  effects.  He 
becomes  sleepy,  loses  control  of  his  muscles,  and  staggers  if 
he  tries  to  walk;  finally  he  may  become  totally  intoxicated, 
in  which  condition  his  brain  has  become  so  completely  para- 
lyzed that  it  no  longer  has  control  over  his  body.  In  these 
extreme  cases  the  narcotic  action  of  alcohol  is  evident,  but 
between  the  intoxication  and  the  action  of  smaller  amounts 
(as  in  the  case  of  the  moderate  drinker),  the  differences  are 
of  degree  rather  than  of  kind. 

One  physiologist  found  after  a  dinner  at  which  he  had 
taken  light  wines,  in  amount  not  sufficient  to  have  any  ap- 
preciable effect  upon  him,  that  either  his  senses  or  his  muscle 
control  had  become  dulled,  as  shown  by  the  fact  that,  if  he 
went  shooting  at  such  a  time,  he  always  shot  behind  the  birds, 
not  being  quick  enough  in  his  judgment  or  action  to  allow 
for  their  flight. 

The  German  physicist,  Helmholtz,  found  that  if  he  had  a 
difficult  problem  to  think  out,  he  must  let  alcohol  entirely 
alone,  for  even  the  smallest  quantity  destroyed  the  keen  edge 
of  his  thinking  powers,  and  prevented  him  from  doing  his  best. 

Careful  observations  have  shown  further  that  in  work  re- 
quiring accuracy,  e.  g.  adding  figures  or  setting  type,  the  use 
of  a  very  small  amount  of  any  kind  of  alcoholic  drink  impairs 
a  person's  efficiency,  making  it  impossible  for  him  either  to  do 
so  rapid  or  so  exact  work  as  usual.  These  illustrations  are 
sufficient  to  show  that  even  from  the  first  the  use  of  alcohol 
acts  as  a  narcotic  upon  brain  functions  and  that  its  apparent 
stimulating  action  is  misleading,  due  to  results  which  are  the 
direct  outcome  of  its  narcotic  action,  e.  g.  dulling  sensibility^ 
relaxing  the  blood  vessels  and  withdrawing  self  restraint. 


A  CLEAR  MIND  THE  NEED  OF  THE  DAY  335 

Insurance  companies  have  found  by  recent  carefully  col- 
lected statistics  that,  on  the  average,  drinkers  are  shorter  lived 
than  abstainers.  It  is  not  surprising  that  these  companies 
will  not  insure  the  lives  of  hard  drinkers,  but  they  have  also 
found  that  the  moderate  drinker  has  a  shorter  life  than  the 
total  abstainer. 

The  great  business  enterprises  of  this  country  have  realized 
the  sapping  influence  and  dangerous  tendencies  of  the  use  of 
alcohol.  Of  seven  thousand  industrial  concerns  questioned 
in  this  respect,  75%  when  engaging  employees  take  into  con- 
sideration the  question  of  their  use  of  alcoholic  drinks.  Over 
half  refuse  to  employ  persons  in  certain  positions  if  they  use 
alcohol.  The  large  railroads  exclude  from  places  of  respon- 
sibility those  addicted  to  it,  and  banks  will  generally  dis- 
charge an  employee  if  they  find  him  frequenting  saloons.  In 
short,  a  person  is  now  seriously  handicapped  in  getting  a 
good  start  in  life  if  he  is  accustomed  to  use  alcohol  in  any 
form.  He  must  frequently  cease  to  strive  for  good,  respon- 
sible positions  and  be  content  with  those  below  the  grade  he 
could  otherwise  reach.  Moreover,  physicians  in  recent  years 
are  prescribing  alcohol  less  and  less  as  a  medicine,  many  of 
them  being  convinced  that  its  use  for  most  purposes  is  futile. 
According  to  a  report  of  the  British  Medical  Society,  with 
those  persons  over  twenty-five  years  of  age  who  use  alcohol 
habitually,  life  is  shortened  on  an  average  of  about  ten  years, 
and  the  injury  to  the  young  is  still  greater. 

'The  best  bred  man  indulging  in  wine  with  permissible 
moderation  no  more  escapes  the  minor  psychical  changes 
induced  by  it  than  does  the  meaner  slave  fail  of  its  sense- 
destroying  power  when  he  drinks  till  he  remembers  his  misery 
no  more.  In  the  case  of  the  former  the  mental  changes  in- 
duced will  never  attain  the  degree  when  self  respect  and  social 
conduct  are  outraged,  and  they  will  pass  unnoticed  by  all 
except  those  who  are  keen  observers  of  their  own  mental 
states.''  (Abd) 


336 


ADVANCED  PHYSIOLOGY 


It  may  seem  a  little  strange  to  class  disease  germs  and 
alcohol  together  as  man's  greatest  foes,  but  it  is  really  stranger 
that  while  we  all  agree  to  fight  the  one  persistently,  a  con- 
siderable portion  of  mankind  prefers  to  play  with  or  indulge 
the  other.  Everyone  who  understands  the  nature  of  disease 
recognizes  the  need  of  fighting  its  agents  or  germs,  but  vast 
numbers  of  people  welcome  rather  than  struggle  against  the 
dangers  of  alcoholism.  The  reasons  for  this  attitude  are 
many,  but  one  of  them  is  that  many  fail  to  realize  that  the 
microscopic  germs  and  the  alcohol  appetite  are  equally 
menaces   to   health   and   happiness. 

Yet  any  one  who  will  open  his  eyes  to  the  conditions  around 
him  will  see  clearly  enough  that  alcholism  is,  in  the  majority 
of  cases,  associated  with  disease,  for  the  reason  that  it  lowers 
one's  powers  of  resistance.     Besides  shortening  his  own  exis- 
tence, the  man  who  drinks  much  is  living  only  part  of  his 
normal  life,  for  his  mind  is  constantly  in  a  state  of  partial 
stupefaction  brought  on  by  the  influence  of  this  paralyzing 
drug.     The  old  toper  has  lost  the  use  of  his  most  valuable 
possession,    while   the   moderate   drinker   is   endeavoring   to 
meet  life  with  slightly  impaired  mental  capacity  and  physical 
powers.     Many  a  youth  begins  with  a  little  beer  or  wine  in] 
the  desire  to  be  ''social,"  to  do  as  others  are  doing,  and  in- 
advertently develops  a  habit  which  places  him  upon  a  lowei 
plane  of  possibility  and  action  than  he  would  otherwise  have] 
attained.     Probably  there  is  no  drunkard  who,  in  youth,  did! 
not  have  his  good  intentions,  his  resolutions  and  ambitions  t( 
be  and  to  do  good,  but  he  trifled  with  them.     It  is  never  pos- 
sible to  predict  whether  or  not  one  will  become  a  victim  of] 
this  appetite,  for  persons  with  apparently  the  strongest  will 
are  often  those  who  yield  most  readily.     The  desire  for  alcohol 
is  an  insidious  one  which  grows  slowly,  usually  without  the] 
consciousness  of  the  individual,  until  it  becomes  too  stronj 
for  him  or  until  he  ceases  to  care  whether  he  masters  it  or  notJ 
Whole  families  are  wiped  out  by  the  evils  which  come  fromJ 


A  CLEAR  MIND  THE  NEED  OF  THE  DAY  337 

its  use,  and  hundreds  of  thousands  of  individuals  are  de- 
prived of  one  or  more  years  of  useful  and  enjoyable  life  by 
imprisonment  for  crime  committed  while  under  the  influence 
of  alcohol. 

There  are  other  foes  with  which  we  have  to  contend  in  our 
efforts  to  make  life  a  success,  but  none  is  greater  than  these 
two.  The  person  who  does  achieve  success,  both  in  his  outer 
and  in  his  inner  life,  is  the  one  who  learns  to  keep  his  body  in 
health  and  his  mind  clear.  The  intellect  is  man's  most  pre- 
cious possession,  and  in  weakening  it,  alcohol  is  attacking 
him  at  the  very  point  on  which  he  must  place  his  dependence 
if  he  is  to  carry  on  a  successful  ^'struggle  for  existence." 

Tobacco. — The  formation  of  the  tobacco  habit  also  pre- 
sents a  question  difficult  for  some  young  people  to  settle. 
The  action  of  tobacco  upon  the  body  is  a  more  or  less  com- 
pUcated  one,  and  is  not  the  same  in  all  individuals.  Tobacco 
contains  a  poison,  nicotine,  which  has  a  powerful  influence  on 
nerve  cells. 

The  physical  effect  of  the  use  of  tobacco  depends  upon  the 
quantity  used,  and,  as  we  have  just  said,  upon  the  individual 
user.  If  very  small  amounts  are  used  it  is  doubtful  whether 
there  is  an  appreciable  result,  and  the  injury  may  not  be 
recognized.  Whatever  influence  it  does  have  is  bad,  es- 
pecially for  young  people.  If  large  quantities  are  consumed, 
the  effect  is  frequently  noticeable  in  an  abnormal  heart  action 
and  in  the  stupefying  of  the  brain.  The  "tobacco  heart," 
the  "cigarette  heart,"  have  become  well  known  terms  which 
the  physician  appUes  to  certain  symptoms  due  to  the  exten- 
sive use  of  tobacco. 

The  effect  of  tobacco  upon  those  who  have  not  attained 
their  full  growth  is  probably  always  injurious.  The  evidence 
is  complete  that  its  use  by  such  persons  prevents  the  full  and 
proper  development  of  the  body,  and  that  a  boy  who  smokes 
constantly  is  stunted  in  his  growth.  In  intellectual  power, 
too,  young  people  seem  to  be  injured  by  the  tobacco  habit 


838 


ADVANCED  PHYSIOLOGY 


A  careful  study  of  the  records  made  by  college  students  shows 
that  those  who  habitually  use  tobacco  are,  on  the  average, 
mentally  inferior  to  those  who  do  not  have  that  habit.  The 
brightest  and  most  independent  are  most  likely  to  avoid  it. 
After  one  reaches  maturity,  i.  e.  after  twenty-five  years  or  so, 
the  effect  of  tobacco  smoking  is  not  so  noticeable,  but  for  all 
persons  of  student  age  the  habit  is  very  unwise,  and  some- 
times disastrous.  Moreover,  employers  of  boys  find  the  cigar- 
ette smoker  decidedly  inferior  to  his  cleaner  companions,  and 
this  inferiority,  generally  speaking,  may  be  said  to  persist  in 
later  life.     The  smoker  is  often  incapacitated  for  fine  work. 


MEDICINES 

In  spite  of  all  one's  attempts  to  keep  himself  in  proper 
health,  he  does  not  always  succeed,  and  almost  everyone  is 
occasionally  ill.  There  is  a  very  general  feeling  that  if  one 
is  ill  the  necessary  thing  is  to  take  a  dose  of  medicine.  People 
have  a  notion  that  medicine  in  some  mysterious  way  will  cure 
disease  no  matter  what  its  cause,  and  sometimes  no  matter 
what  the  medicine.  Much  evil  results  from  this  ignorant 
idea.  For  ordinary  ills  there  is  always  a  cause,  and  the  proper 
course  is  to  remove  the  cause  rather  than  to  take  medicine.  If, 
for  example,  one  suffers  from  indigestion,  he  should  endeavor 
to  change  his  food  habits  or  his  food,  or  to  take  more  exercise 
rather  than  to  continue  in  the  old  way  and  rely  upon  medicine 
to  cure.  Indeed,  most  of  the  little  ills  in  life  can  be  readily 
mastered  by  a  change  of  habit,  without  medicine.  Medicine  i 
has  its  uses,  beyond  doubt,  but  it  is  very  unwise  and  unsafe] 
for  the  untrained  person  to  administer  it. 

Especially  is  it  a  mistake  to  buy  and  use  the  numerous! 
so-called  ^^ patent  medicines, ^^  extensively  advertised  and 
claiming  to  cure  a  long  list  of  troubles.  This  does  not  mean] 
that  none  of  them  has  any  value,  but  that  many  contain] 
powerful  drugs,  alcohol  or  opium,  which  cannot  be  safely] 
used  by  anyone  and  certainly  not  without  the  advice  of  aj 


A  CLEAR  MIND  THE  NEED  OF  THE  DAY  339 

physician.  Beyond  a  few  simple  remedies  we  should  leave 
the  giving  of  medicines  to  a  physician  who  understands  that 
they  are  merely  a  help  and  not  a  cure  for  disease  and  that 
the  patient  is  frequently  better  off  without  them. 

If  one  recovers  from  disease  it  is  often  because  the  body 
cures  itself  by  its  own  vitality.  Medicines  may  assist,  but 
a  person  really  cures  himself.  The  taking  of  too  much  medi- 
cine without  the  advice  of  a  physician  is  one  of  the  great 
faults  of  the  American  people.  Every  young  person  in  prep- 
aration for  life  should  make  up  his  mind  that,  if  properly 
treated,  his  body  can  take  care  of  itself  without  the  use  of 
drugs.  If  it  is  ill,  except  when  the  trouble  is  a  germ  disease, 
the  difficulty  usually  lies  in  an  improper  mode  of  living,  and 
this  cannot  be  cured  by  medicine.  Medicines,  properly 
administered  by  one  who  understands  them,  are  useful,  but 
miscellaneously  used  by  others,  they  are  productive  of  a  vast 
deal  of  harm  and  an  incalculable  waste  of  money. 


CHAPTER  XXI 

ORGANS  OF  SPECIAL  SENSE— THE  EYE 

In  a  preceding  chapter  we  noted  that  every  sensory  nerve 
ends  in  a  special  bulb,  or  corpuscle,  and  some  of  these  were 
shown  in  Figures  117,  118  and  162.  The  endings  there  rep- 
resented were  very  simple,  having  only  simple  functions  to 
perform,  like  that  of  receiving  touch,  heat  or  pain  stimuli. 
There  are  other  sensory  nerves,  particularly  some  of  those 
coming  out  of  the  brain  directly,  which  have  very  elaborate 
endings,  usually  spoken  of  as  organs  of  special  sense.  The 
most  important  of  these  are  the  eye  and  the  ear. 

EXTERNAL  PARTS  OF  THE  EYE 

The  eye  (Fig.  165)  is  set  into  a  cavity  in  the  skull,  the  eye 
socket,  which  is  lined  with  a  layer  of  fatty  tissue  serving  as  a 
cushion.  The  eyeball  is  not  perfectly  round,  since  over  the 
colored  portion  at  the  front  the  sphere  bulges  slightly,  although 
not  enough  to  be  noticed  ordinarily. 

Externally  the  eyes  are  protected  by  the  lids,  which  are 
folds  of  the  skin  of  the  face  supplied  with  muscles  to  permit 
movement  in  winking;  Fig.  166.  In  the  process  of  moving 
the  lids  two  muscles  especially  are  concerned:  one,  the  so- 
called  orbicular,  is  a  circular  muscle  running  around  in  both  the 
upper  and  the  lower  lids;  the  other,  the  levator,  is  in  the 
upper  lid,  and  runs  upward  from  the  edge  and  raises  it  after 
the  orbicular  has  closed  the  eye.  The  lower  lid  moves  very 
little,  and  is  not  drawn  downward  by  any  sp«^al  muscle. 

At  the  inner  corner  of  each  eye  is  a  little  whitish  mass  of 
tissue  which  is  of  doubtful  value  in  man;  in  birds  and  some  rep- 
tiles, a  corresponding  structure  is  a  third  eyelid,  which  is  trans- 
parent and  can  be  closed  while  the  others  remain  motionless. 

ii40 


ORGANS  OF  SPECIAL  SENSE— THE  EYE  341 

The  lashes  on  the  edges  of  the  Uds  protect  the  eyes  some- 
what from  dust.  The  inner  surface  of  the  Hds  is  really  nothing 
but  the  external  skin  folded  back  underneath,  but  it  is  pro- 
vided with  special  glands  which  are  not  present  in  the  ordinary 
surface  of  the  skin.  These  Meibomian  glands  are  arranged  in 
little  clusters,  with  their  openings  near  the  edges  of  the  hds 
(Fig.  166)  and  are  more  abundant  in  the  upper  than  in  the 
lower  lid.  Their  secretion  is  oily  and  by  mixing  with  the 
more  watery  product  of  the  tear  glands  prevents  the  rapid 
drying  of  the  latter  as  it  is  spread  over  the  eye  in  a  thin 
layer  when  one  winks. 

A  tear,  or  lachrymal,  gland  is  located  just  above  the 
outer  corner  of  each  eye.  It  is  about  three-quarters  of  an 
inch  long,  one-quarter  of  an  inch  wide,  and  the  material  which 
it  secretes  is  poured  under  the  upper  lid  through  six  or  seven 
tiny  canals.  This  lachrymal  secretion  is  largely  water,  with 
a  little  salt,  and  the  smearing  of  the  secretion  over  the  eye- 
balls in  winking  prevents  the  delicate  membranes  of  the  eye 
from  becoming  dry,  and  consequently  more  or  less  opaque. 

The  liquid  material  secreted  by  the  several  glands  about 
the  eye  runs  away  through  two  tiny  openings  in  the  inner 
corner  of  each  eye  into  canals,  which  unite  into  the  lachrymal 
duct,  leading  to  the  nose  chamber.  A  downward  current  is 
produced  in  these  canals  by  cilia  which  project  into  them  on 
all  sides. 

Muscles  which  Move  the  Eye. — The  movement  of  the  eye  is 
effected  by  six  different  muscles,  all  of  which  are  attached  to 
the  eyeball  at  different  points  back  of  the  lids:  Fig,  165.  Four 
of  these,  one  above,  one  below,  one  outside  and  one  inside,  are 
called  rectus  muscles  and  pass  from  their  attachments  to  the 
eyeball  directly  back  to  a  point  in  the  deepest  part  of  the 
socket.  The  one  next  the  nose  is  called  the  internal  rectus; 
the  outer,  the  external  rectus;  the  upper  is  the  superior,  and  the 
lower  the  inferior  rectus.  The  other  two  muscles  are  called  the 
obHques.     The  inferior  oblique  is  attached  to  the  lower  sur- 


342 


ADVANCED  PHYSIOLOGY 


face  of  the  eyeball  and  to  the  bones  on  the  side  of  the  nose. 
The  superior  oblique  muscle  on  the  upper  surface  of  the  eye 
passes  inward  toward  the  hose,  but  on  reaching  it,  its  tendon 


Inferior 
Oblique  muscle 


Superior 
Oblique  muscle 


Opfic  ,.. 

ner'ye 
infer.  Reef  us 


/^ExtenRecfus 
Super:     • 


Fig.   165. — Diagram 

Showing  the  eyes  in  position  in  their  sockets,  the  muscles  that  move  them  and 
the  optic  nerves.  (Fox) 

goes  through  a  loop,  which  acts  as  a  pulley,  and  then  passing 
backward  is  attached  near  the  same  place  as  the  rectus  muscles. 

Demonstration. — The  muscles  which  move  the  eye  can  be  well  shown 
by  use  of  the  eye  of  a  dog-fish.  The  skull  is  cartilaginous  and  easily  cut 
away,  and  the  muscles  are  diagrammatically  plain.     Appendix,  Section  30. 

All  movements  either  in  a  vertical  or  a  horizontal  plane 
must  be  made  by  the  rectus  muscles,  and  movements  not  ex- 
actly in  either  of  these  planes  may  be  produced  by  the  com- 
bined action  of  two  or  more  of  them.  It  would  seem  that 
their  contraction  would  produce  all  movements  the  eyes  ever 
make.     As  a  matter  of  fact,  however,  the  oblique  muscles  are 


ORGANS  OF  SPECIAL  SENSE— THE  EYE 


343 


'uscIp 


constantly  used,  not  alone,  but  to  adjust  the  movements  of 
the  rectus  muscles  more  accurately. 

The  extreme  delicacy  with  which  these  muscles  work  is 
not  usually  appreciated. 
Especially  remarkable  is 
the  accuracy  with  which 
they  move  when  one  is 
reading  a  printed  page. 
The  eye  is  perfectly  di- 
rected to  a  certain  letter, 
to  comma  or  period,  and 
then  as  suddenly  turned, 
it  may  be  only  a  hair's 
breadth,  and  the  process 
repeated  thousands  of 
times  in  an  hour,  yet 
always  with  the  most  re- 
markable precision. 


tluscle 


Olancf 


Fig.  166. — A  section  through  the 

UPPER  EYELID 
Highly  magnified.    (Fuchs) 


STRUCTURE 
OF  THE  EYE  PROPER  -- —         >-y^      tashcs 

The  Sclerotic  and  Cho- 
roid Coats.  — On  the  ex- 
terior of  the  front  of  the 
eye  is  an  extremely  thin 
layer  of  tissue  called  the  conjunctiva.  This  is  continuous 
with  the  lining  of  the  eyelids,  and  its  transparency 
makes  it  imperceptible.  Beneath  the  conjunctiva  is  a 
thicker  layer  which  extends  over  the  whole  eyeball, 
serving  to  protect  it  and  keep  it  in  shape.  In  front, 
this  also  is  perfectly  transparent;  but  beginning  with  the 
"white"  and  passing  about  the  rest  of  the  sphere,  it  is  tough 
and  opaque.  The  transparent  portion  in  front  is  called  the 
cornea,  the  rest  the  sclerotic  coat;  Fig.  167, 


344 


ADV.\XCED  PHYSIOLOGY 


Beneath  the  sclerotic  and  cornea  is  the  choroid  coat;  Fig. 
167.  It  contains  a  large  number  of  blood  vessels  and  is  the 
principal  nourishing  layer  of  the  eye.  The  choroid  covers 
the  whole  ball  save  a  small  spot  exactly  in  front,  the  pupil. 
Around  the  pupil  is  a  colored  area,  blue,  brown  or  black,  as 
the  case  may  be,  called  the  iris.  The  pigment  area  of  the  iris 
is  for  the  purjxxse  of  shutting  out  all  Ught  except  an  amount 
sufficient  to  stimulate  properly  the  nerves  of  sight.  When  the 
light  is  dim,  more  must  be  admitted  to  produce  the  requisite 
degree  of  stimulation;  consequent!}'  the  iris  is  provided  with 
muscles  by  whose  contraction  and  relaxation  the  aperture  of  the 

pupil  is  made  smaller 
or  larger.  Certain  other 
muscles  belonging  to 
the  choroid  coat  will 
be  mentioned  in  a 
later  paragraph  in  con- 
nection with  the  focus- 
ing mechanism  of  the 
eyes. 

The  Retina. — Inside 
the  choroid  covering 
is  the  retina,  the  only 
layer  of  tissue  in  the 
eye  which  is  sensitive 
to  lights  This  does  not  go  entirely  about  the  eye,  being 
absent  in  front  in  the  region  of  the  iris  and  pupil. 

The  Vitreous  and  Aqueous  Humors. — Filling  up  the  center 
of  the  eye,  and  making  the  whole  organ  spherical,  is  a  mass  of 
clear,  jelly-Uke  material,  the  vitreous  humor.  In  front  in  the 
space  between  the  iris  and  the  cornea  is  also  a  mass  of  clear, 
faansparent  material,  the  aqueous  humor,  which  causes  the 
cornea  to  protrude  slightly;  Fig.  167. 

The  Lens. — The  lens  also  is  made  of  perfectly  clear,  trans- 
parent material  of  the  consistency  of  thick  jelly.     In  shape  it 


Fig.  167. — Diagsam 
a  section  throq^  ikm  vyAaB 


ORGANS  OF  SPECIAL  SENSE— THE  EYE  346 

is  like  ordinary  glass  lenses,  though  more  convex  on  both  sides. 
If  taken  out  of  the  eye,  the  lens  still  has  enough  rigidity  of  its 
own  to  keep  its  shape.  It  is  in  the  same  cavity  with  the  vitre- 
ous humor  in  a  vertical  plane  just  back  of  the  iris.  Note  in 
Figure  167  that  the  lens  is  more  convex  on  the  back  than  on 
the  front  side,  and  that  at  its  edges  it  is  held  in  place  by  slender 
ligaments  which  run  outward  into  the  choroid  layer.  These  are 
collectively  called  the  suspensory  ligament,  which  must  be 
thought  of  as  a  thin  sheet  of  ligamentous  tissue  going  entirely 
about  the  lens  border,  rather  than  as  a  cord  attached  to  any 
one  or  several  points.  It  swings  the  lens  into  position,  by 
tension  on  its  edges  in  every  direction. 

THE  FORMATION  OF  IMAGES 

When  one's  eyes  are  open,  there  is  formed  upon  the  retina 
a  picture  or  image  of  the  object  in  front  of  the  eye.  The 
secret  of  this  picture  formation  lies  entirely  in  the  lens  and 
the  cornea,  more  especially  in  the  former. 

Everyone  knows  that  light,  reflected  from  trees,  buildings, 
people  or  other  objects,  on  passing  through  the  lens  of  a  photo- 
grapher's camera  produces  an  impression  on  the  sensitive 
plate  within.  If  we  compare  this  plate  to  the  retina  of  the 
eye,  and  the  lens  to  the  lens  of  the  eye,  the  similarity  between 
the  eye  and  the  camera  is  very  striking.  In  Figure  167  is 
shown  the  arrangement  of  the  lens  and  the  retina.  Straight 
lines  show  the  direction  which  rays  of  light  take  in  the  eye. 
In  this  case  it  is  supposed  that  the  object  seen  is  a  point  and 
that  the  rays  of  light  entering  the  eye  are  parallel.  It  will 
be  seen  that  these  rays  after  passing  through  the  lens  bend 
from  their  parallel  direction  and  come  together.  It  is  plain 
that  they  must  meet,  otherwise  they  would  strike  many 
different  parts  of  the  retina  at  the  same  time,  and  a  large 
number  of  points  instead  of  one  would  be  seen.  Each  would 
be  seen  indistinctly,  too,  since  the  light  would  be  so  sub- 
divided as  not  to  be  intense  at  any  one  place  on  the  retina. 


346 


ADVANCED  PHYSIOLOGY 


v.  Glass 


The  law  which  makes  the  rays  bend  as  they  go  through 
the  lens,  and  causes  them  to  form  an  image  on  the  other  side 
is  very  simple.  When  a  ray  of  light  passes  from  any  point 
through  air,  it  always  passes  in  a  straight  line;  but  if  it  enters 
a  transparent  substance  like  glass,  which  is  denser  than  air, 
it  is  usually  turned  to  one  side.  If  it  enters  the  glass  per- 
pendicularly, it  still  goes  on  in  a 
straight  line  (Fig.  168  C-c);  but 
if  it  enters  at  an  angle  it  is  always 
bent  to  one  side,  and  the  greater 
the  angle  at  which  it  enters  the 
more  it  is  bent  (Fig.  168  A-a, 
B-h) .  After  it  has  passed  through 
the  glass  and  as  it  comes  out  on 
the  other  side,  it  is  bent  again. 

So  it  happens  that  rays  of  light 
in  passing  through  glass  at  an 
acute  angle  to  its  surface  are  sure 
to  change  their  direction.  One 
often  sees  this  principle  illustrated  when  he  looks  out  of 
doors  through  a  window.  If  the  light  from  the  objects  thus 
seen  comes  to  him  through  a  more  or  less  irregular  piece  of 
ordinary  window  glass,  and  especially  if  it  comes  through 
slantwise,  the  object  seems  to  be  very  much  distorted.  If 
one  sees  things  through  a  piece  of  plate  glass  there  appears 
to  be  far  less  disturbance  of  the  image  than  in  the  case  of  un- 
even glass,  yet  when  the  plate  glass  is  bevelled  along  the  edge, 
objects  which  can  be  seen  through  the  general  surface  plainly, 
cannot  be  seen  at  all,  or  only  in  a  distorted  manner  through 
the  bevelled  area.  Light  from  the  object  in  going  through  the 
bevelled  surface  has  been  thrown  out  of  its  path. 

Let  us  now  notice  the  effect  of  a  lens  upon  rays  of  hght.' 
The  surfaces  of  the  lens  are  curved,  i.  e.  parts  of  spheres. 
From  Figure  169  it  will  be  seen  that  if  parallel  rays  enter  the 
^  For  demonstration  see  Appendix,  Sections  32  and  33, 


Air 


Fig.  168. — Diagram 

Showing  the  refraction  of  light 
while  passing  through  a  piece  of 
glass  with  parallel  surfaces. 


ORGANS  OP  SPECIAL  SENSE— THE  EYE 


347 


lens,  they  enter  it  at  different  angles,  and  are  consequently 
bent  in  different  directions  and  that  when  they  emerge  they 
are  bent  again,  each  differently  from  the  others.  Now  when 
the  surfaces  of  the  spheres  are  perfect  curves,  the  angles  at 
which  the  rays  enter  and  leave  it  are  such  that  after  passing 
through  they  are  bent  toward  one  point  where  all  of  the  rays 
meet;  Fig.    169.      If    a 

sheet  of  paper  is  held  at        7^ 

this    focus,    a    point   of       /— V 

light  will  show  upon  it. 
Figure  170  shows  a 
slightly  different  con- 
dition. Here  A  is  a 
point  of  light  near  the 
lens,  and  from   it   light 

rays  pass  outward  in  all  directions.  The  rays  are  not  parallel 
as  in  the  former  instance  but  diverging;  yet  they  are  bent  as 
before,  as  they  are  passing  through  the  lens  and  are  also 
brought  toward  one  point  a,  at  which  they  focus.  But  it  will 
be  noticed  that  this  focus  is  farther  from  the  lens  than  the 


Fig.  169. — Diagram 

Showing  the  manner  in   which   a   lens  bends 
rays  of  light  so  as  to  bring  them  to  a  focus. 


r::^^ 


Fig.  170. — ^Diagram 

Showing  the  relative  position  of  the  foci  formed  by   parallel  rays  of  light  and  by 
diverging  rays  of  light  coming  from  objects  near  the  lens. 

focus  of  parallel  rays,  /.   If  the  point  of  light  is  brought  nearer 
the  lens,  at  B,  its  focus,  h,  will  be  still  farther  away. 

There  is  a  way  in  which  the  image  can  be  brought  nearer 
to  the  lens  and  the  focal  distance  not  be  lengthened.  If  the 
lens  be  replaced  by  one  of  greater  curvature,  i.  e.  more  bulging, 
it  will  bring  the  rays  to  a  focus  sooner.     If  on  the  other 


348 


ADVANCED  PHYSIOLOGY 


Fig.  171. — Diagram 

Showing  the  method  of  the  formation  of  an  image 

by  a  lens. 


hand  it  is  replaced  by  one  of  less  curvature,  it  will  bend  them 
less  sharply  and  bring  them  to  a  focus  at  a  greater  distance 
from  the  lens.  If,  however,  the  lens  be  concave,  the  rays 
will  be  scattered  instead  of  being  brought  to  a  focus.  It  is 
important  that  these  points  be  clearly  seen,  in  order  that  one 
may  understand  the  accommodation  of  the  eye. 

If,  instead  of  a  single  point  giving  out  light,  there  is  an 
object  of  some  size,  the  action  of  the  lens  is  essentially  the 

same.  Suppose  that 
the  object  is  a  candle 
flame  (Fig.  171);  the 
tip  of  the  Hght,  A,  is 
a  point  and  the  rays 
passing  from  it  will, 
of  course,  be  focused 
at  a  point,  a.  The 
base  of  the  light  isi 
another  point,  BA 
which  will  be  focused  at  b.  In  the  center  of  the  candle  we] 
might  select  another  point  which  would  then  be  focused] 
between  a  and  b.  The  whole  candle  and  its  flame  arej 
made  up  of  points,  each  of  which  will  be  focused  at  a  cor- 
responding point.  If,  therefore,  a  piece  of  paper  or  a  screen, 
be  placed  at  the  line,  a-b,  we  shall  find  an  image  of  the  candle] 
flame  upon  it.  The  image,  however,  will  be  upside  down, 
is  evident  from  the  figure. 

In  the  human  eye  an  image  is  formed  in  exactly  the  same| 
manner.  The  lens  focuses  the  light  that  passes  through  it] 
and  produces  an  image  at  a  certain  distance  behind  it.  Inj 
a  normal  eye  the  retina  is  at  just  the  proper  distance  so  that] 
the  rays  of  Hght  are  focused  upon  it,  and  the  image  thus 
formed;  Fig.  172.  Since  this  image  is,  of  course,  up  side! 
down,  one  naturally  asks,  why  do  we  not  see  things  in  in-j 
verted  positions.  This  question  arises  from  the  false  im-! 
pression  that  one's  brain  pictures  things  just  as  they  occur  on' 


ORGANS  OF  SPECIAL  SENSE— THE  EYE 


348 


I 


the  retina,  as  if  the  brain  were  looking  at  the  image  on  the 
retina.     The  exact  process  by  which  the  brain  perceives  the 
image  is  compHcated,  and  not  entirely  known.     For  our  pur- 
pose it  is   sufficient  to  say  that 
although   the    image  is  certainly 
inverted  on  the  retina,  after  the 
impression  has  reached  the  brain, 
it  is  interpreted  so    that  we  see 
things  as  they  are. 

Accommodation. —  Every  one 
knows  that  it  is  perfectly  pos- 
sible to  look  at  a  spot  on  the 
window  glass  and  see  it  clearly, 
and  at  the  same  time  see  indis- 
tinctly whatever  there  may  be  beyond  the  glass,  trees,  build- 
ings etc.  If  one  chooses  he  can  give  all  his  attention  to  the 
trees  and  see  them  very  clearly,  at  the  same  time  seeing  very 


Fig.  172. — Diagram 

Showing  the  formation  of  an   im- 
age upon  the  retina. 


Fig.  173. — Diagram 

Showing  the  effect  of  different  lenses  in  changing  the  position  of  the  focus  of  light' 
and  illustrating  how  a  change  of  the  lens  is  necessary  if  objects  at  different  dis- 
tances are  to  be  focused  upon  a  screen. 


indistinctly  the  window  glass  and  frame.  When  he  changes 
his  attention  from  one  to  the  other  he  is  conscious  that  some- 
thing is  taking  place  in  his  eyes,  and  that  it  requires  part  of 


350  ADVANCED  PHYSIOLOGY 

a  second,  at  least,  for  the  change  to  be  made.  This  process 
is  called  accommodation,  and  occurs  almost  entirely  in  the 
lens,  although  the  front  of  the  cornea  is  also  sUghtly 
modified. 

The  form  which  a  lens  must  take  when  the  object  viewed 
is  near  at  hand,  as  compared  with  its  form  when  the  object  is 
far  away,  is  shown  in  Figure  173.  When  a  point  is  near  the 
lens,  as  at  A,  the  rays  of  light  going  from  it  will  diverge 
rapidly.  In  order  to  bring  them  to  a  focus  at  the  distance 
of  the  screen  or  retina,  they  must  be  bent  very  decidedly 
inward.  It  is  also  evident  that  if  a  point  is  farther  away  from 
the  lens,  as  at  B,  the  rays  will  not  be  diverging  as  rapidly 
when  they  reach  the  lens,  and  not  being  turned  from  their 
course  as  much  as  those  from  A,  will  come  to  a  focal  point  in 
front  of  the  screen  or  retina  at  h.  Moreover,  we  have  already 
noticed  that  the  more  bulging  or  convex  the  lens,  the  more 
sharply  the  light  rays  going  through  it  will  be  bent  from  their 
paths.  If,  therefore,  a  flatter  lens  is  substituted,  like  the  one 
marked  I,  which  has  a  curvature  only  suflacient  to  bring  rays 
from  point  B'  to  a  focus  at  6',  the  rays  from  point  A^  will  not  be 
sufficiently  bent  and  will  be  focused  behind  the  screen  at  a\ 
But  if  a  more  convex  lens  is  substituted,  like  the  one  at  l\ 
the  rays  from  both  A^  and  B^  will  be  focused  in  front  of  the 
screen  at  a''  and  6''.  Thus  a  lens  of  a  definite  curvature  is 
necessary  for  properly  focusing  light  from  anj^  particular  point. 
If  one  wishes  to  look  at  a  distant  point  after  examining  a 
near  one,  the  lens  must  be  flattened;  and  when  the  attention  is 
turned  from  a  distant  point  to  a  near  one,  a  more  convex 
lens  is  necessary. 

Mechanism  of  Accommodation. — In  the  eye  it  is  not  neces- 
sary to  replace  one  lens  with  another,  for  the  lens  of  the  eye 
is  not  rigid  like  glass,  but  can  change  its  shape  from  a  thin, 
flattish  to  a  very  convex  form.  Attached  to  the  edge  of  the 
lens  and  holding  it  to  the  choroid  layer,  we  have  noticed  the 
suspensory  ligament.     This  is  under  tension,  and  as  a  result 


ORGANS  OF  SPECIAL  SENSE— THE  EYE 


351 


is  pulling  outwards  on  the  edge  of  the  lens  in  every  direction; 
Fig.  167.  Since  the  lens  is  somewhat  soft,  this  outward  pull 
tends  to  flatten  it.  In  this  shape,  the  lens  is  in  condition  for 
focusing  on  the  retina  rays  of  light  coming  from  a  dis- 
tance. 

If  the  object  viewed  is  near,  as  it  is  in  reading  or  writing, 
the  lens  must  be  more  convex.  All  that  is  needed  to  make  it 
so  is  to  loosen  the  ligament,  when  the  lens  of  its  own  elasticity 
will  bulge,  and  assume  the  necessary  convexity.  For  every 
different  distance  the  tension  of  the  Ugament  must  be  changed 
accurately  and  almost  instantaneously,  so  that  the  convexity 
of  the  lens  may  be  exactly  correct. 
This  regulation  of  the  suspensory  lig- 
ament is  accomphshed  by  the  so-called 
ciliary  muscle,  (Fig.  174),  one  end  of 
which  is  attached  to  the  choroid  coat 
behind  the  point  where  the  suspensory 
Ugament  arises,  the  other  end  fusing 
with  the  iris  and  the  inner  layers  of  the 
cornea.  When  this  muscle  contracts, 
it  is  easy  to  see  that  the  choroid  layer 
will  be  pulled  forward,  the  ligament 
will  become  loose  and  the  lens  will 
"bulge,"  taking  the  shape  of  the  dotted 
line  in  Figure  174.  The  more  the  muscle 
contracts,  the  more  convex  the  lens 
will    become,    and    consequently    the 

nearer  objects  may  be  held  and  yet  be  seen.  There  is,  however, 
a  limit  to  the  nearness  at  which  objects  may  be  seen.  The 
ciliary  muscles  can  contract  only  a  certain  amount,  and  the 
lens  can  become  convex  only  within  certain  limits.  When 
an  object  is  held  too  near  the  eyes,  everything  becomes  blurred 
since  its  light  is  not  focused  on  the  retina.  The  chief  reason 
that  one's  eyes  become  tired  from  reading  is  that  the  ciliary 
muscles  are  weary  from  staying  contracted  during  the  prt?- 


Ciliortf  Muscle.. 


Suspensory 
li^ameirf 


Fig.  174. — Diagram 

Showing  the  method  by  whici: 
the  lens  is  held  by  the  sus- 
pensory ligament,  and  the 
ciliary  muscle  whose  con- 
traction will  loosen  the  liga- 
ment and  allow  the  lenf 
to  bulge. 


352 


ADVANCED  PHYSIOLOGY 


^A=-« 


Fig.  175. — Diagram 
Showing  that  when  parallel  rays  of  light  are 
focused  on  the  retina,  rays  from  near  objects 
will  be  focused  back  of  the  retina. 


longed  period  that  one  has  been  looking  at  the  book  held  neai 
the  eyes. 

Figures  175  and  176  show  what  the  result  would  be  if  the 
lens  of  the  eye  could  not  be  accommodated  to  different  dis- 
tances. There  would  be 
only  one  point  at  which 
objects  could  be  seen 
clearly.  If  parallel  rays 
of  light  are  focused  on 
the  retina  as  in  Figure 
175,  rays  from  points 
near  by,  as  at  A,  will 
be  focused  behind  it. 
If,  however,  rays  from 
an  object  near  the  eye  are 
properly  focused,  as  in 
Figure  176,  objects  farther  away  would  be  indistinct  because 
light  from  them  would  come  to  a  focus  in  front  of  the  retina. 
The  power  of  changing  the  shape  of  the  lens  allows  objects 

at    any    distance    (not    too 
near)  to  be  seen  clearly. 

Near-  and  Farsightedness. 
— The  normal  eye  is  of  such 
shape  that  parallel  rays  of 
light  are  focused  exactly  on 
the  retina;  Fig.  175.  Often, 
however,  a  person's  eyeballs 
are  a  little  too  long  or  the 
lenses  a  little  too  convex 
(Fig.  176),  so  that  enter- 
ing rays  of  light  coming  from  a  distance  are  not  focused 
on  the  retina  but  in  front  of  it,  and  to  be  focused  ex- 
actly on  the  retina,  an  object  must  be  held  close  to  the  eyes. 
Nearsightedness,  or  myopia,  may  result  from  either  of  these 
causes,  and  in  either  case  the  difficulty  may  be  remedied  by 


Fig.  176. — Diagram 

Showing  that  when  near  objects  are 
focused  on  the  retina,  parallel  rays  of 
light  will  be  focused  in  front  of  it. 


ORGANS  OF  SPECIAL  SENSE— THE  EYE 


353 


Fig.    177. — Diagram 

Showing  a  nearsighted  eye  with  a  proper 
lens  for  correcting  the  defect. 


glasses.  The  reason  that  the  nearsighted  person  finds  it  hard  to 
see  distant  objects  distinctly  is  that  the  rays  forming  the  image 
come  to  a  focus  too  quickly  after  entering  the  eye;  if  lenses  of 
just  the  right  curvature  be 
placed  in  front  of  his  eyes,  so 
that  the  rays  are  caused  to 
diverge  a  little  before  reach- 
ing the  eyes  (Fig.  177,  dotted 
lines),  the  rays  will  be  brought 
to  a  focus  at  exactly  the  right 
place.  By  '^fitting  a  person 
with  glasses"  we  simply  mean 
that  extra  lenses  are  chosen 
of  just  the  right  curvature  to  correct  his  particular  trouble. 
Myopia  is  common  among  those  who  read  very  much  or 
use  their  eyes  for  other  work  at  close  range.  To  avoid  devel- 
oping nearsightedness,  one  should  acquire  the  habit  of  hold- 
ing books  at  least  eighteen  inches  from  the  eyes. 

In  farsightedness,  or  hyperopia,  the  conditions  are  just  the 
reverse  of  those  in  nearsightedness.  The  person  cannot  see  a 
near-by  object  clearly  because 
the  lens  is  too  flat  or  the  eye- 
ball too  short.  The  rays  of 
light  going  into  the  eye  come 
together  behind  the  retina,  as 
shown  in  Figure  178.  In  such 
an  eye  even  the  full  contraction 
of  the  ciliary  muscle  may  be 
unable  to  make  the  lens  convex 
enough  to  bend  the  light  rays 
to  a  point  by  the  time  they  reach 

the  retina,  and  consequently  the  image  is  blurred.  If,  how- 
ever, a  sHghtly  convex  spectacle  lens  be  used,  which  will 
turn  the  rays  and  start  them  to  a  point,  the  lens  of  the  eye 
can  do  the  rest;  Fig.  178. 


Fig.  178. — Diagram 

Showing  a  farsighted  eye  with  proper 
correcting  lens. 


354 


ADVANCED  PHYSIOLOGY 


Astigmatism. — We  have  assumed  that  the  surface  of  the  cor- 
nea in  front  and  of  the  lens  behind  it  were  parts  of  true  spheres, 
curving  equally  in  all  directions.  The  majority  of  eyes,  how- 
ever, are  astigmatic,  i.  e.  there  is  somewhere,  either  in  the 
cornea  or  lens,  an  irregularity  so  that  the  combined  shape  of 
these  bodies  is  more  like  that  of  a  football  than  like  a  true 
sphere,  curving  in  a  circle  in  one  direction,  but  in  an  oval  in 
the  other.  As  a  rule  there  is  one  plane  in  which  persons 
with  astigmatic  eyes  can  see  well,  but  in  all  other  planes  the 
image  will  be  blurred;  Fig.  179.  To  remedy  this  very  serious 
defect  it  is  plain  that  neither  a  perfectly  convex  nor  a  per- 


FiG.  179. — Diagram  of  defects  in  an  astigmatic  eye 

Showing  that  rays  from  a  point  are  not  properly  focused.  A,  source  of  light; 
B,  C,  retinal  surface;  D,  lens.  Rays  in  one  plane  come  to  a  focus  at  a  point;  in 
the  other  plane  they  are  distributed  over  B  C  in  a  line. 

fectly  concave  lens  will  suffice.  The  need,  then,  is  for  a  lens 
ground  at  two  different  curvatures,  the  opposites  of  those  in 
the  eye  lens. 

THE  RETINA  AND  ITS  FUNCTIONS 

We  have  seen  that  the  images  of  objects  in  the  external 
world  are  focused  upon  the  retina,  a  fact  which  suggests  that 
this  is  the  sensitive,  i.  e.  the  real  seeing  part  of  the  eye. 

The  actual  thickness  of  the  retina  at  its  thickest  part,  at 
the  back,  is  only  about  one  seventy-fifth  of  an  inch  and  it  is 
much  thinner  than  that  on  the  sides  of  the  eye.     Its  border 


ORGANS  OF  SPECIAL  SENSE— THE  EYE 


355 


near  the  sides  of  the  iris  is  a  mere  frayed  edge  of  tissue.  Yet 
this  thin  layer  is  a  very  compHcated  structure,  a  microscopic 
section  showing  eight  well  defined  layers  or  strata.  Next  to 
the  choroid  coat  is  a  pigment  layer.  At  first  glance  this 
usually  appears  black,  but  when  more  carefully  examined  it 
proves  to  be  made  up  of  granules  of  a  purplish  hue,  a  fact 
which  explains  why  this  material  is  sometimes  called  the 
"visual  purple."  This  pigment  is  not  laid  down  in  an  even 
coating   next    the 

choroid,   but  is   ar-  -^°^^  ^°"^' 

ranged  in  a  kind  of 
mosaic  of  six-sided 
patches. 

Next  the  pigment 
is  a  layer  of  cells  of 
very  peculiar  shape. 
Each  contains  a  nu- 
cleus like  any  other 
cell,  but  has  two 
outgrowths  on  op- 
posite sides;  Fig. 
180.  On  one  side 
a  fibre  extends  and 
ends  in  numerous 
small  branches  or 
arborations;  on  the 
other  side  opposite 
the  fibre,  in  some  a 
rod-like,  in  others  a  cone-like  structure  is  found.  These  rods 
and  cones  are  all  arranged  parallel  with  one  another,  their  ends 
pointed  toward  the  pigment  layer,  the  rods  in  many  cases 
reaching  into  the  pigment.  At  the  back  of  the  eye  the  cones  are 
much  more  abundant  than  on  the  sides  of  the  eyeball,  where  the 
rods  predominate.  In  the  very  center  of  the  back  of  the  eye 
directly  behind  the  pupil,  is  a  minute  area  in  which  there  are 


■  Nerve  Fibns 
Fig.  180. — Section  through  the  retina 

Very  highly  magnified.  The  lower  edge  is  the  om 
toward  the  center  of  the  eye.  The  rods  and  cone? 
are  indirectly  connected  with  the  nerves.   (Cajal) 


850  ADVANCED  PHYSIOLOGY 

only  cones,  and  which  lacks  nearly  all  the  other  layers  of  the 
retina.  It  is  plain  from  its  situation  that  light  coming  directly 
into  the  eye  falls  on  this  spot.  This  is  the  area  of  clearest 
vision,  or  in  scientific  terms,  the  fovea  centralis,  Fig.  167. 

The  other  layers  of  the  retina  are  represented  in  Figure  180, 
but  no  special  description  of  them  will  be  given.  From  the 
figure  it  will  be  noticed  that  from  the  inner  ends  of  the  rod  and 
cone  cells  other  nerve  cells  arise,  which  extend  toward  the  inner 
portion  of  the  retina,  and  are  there  connected  or  closely  as- 
sociated with  nerve  fibres.  Any  impulse,  then,  which  starts 
from  the  rods  and  cones  may  pass  up  through  these  connec- 
tions until  it  reaches  the  nerve  fibres,  and  goes  through  them 
to  the  brain. 

The  nerve  fibres  thus  arise  on  the  innermost  side  of  the 
retina  next  to  the  vitreous  humor.  They  all  pass  toward  the 
back  of  the  eyeball  and  finally  unite  to  form  the  large  optic 
nerve.  This  nerve  passes  through  the  various  coats  of  the 
eyeball  and  then  goes  to  the  brain.  It  does  not  leave  the  eye 
directly  at  the  back,  in  the  line  of  entering  light,  but  on  the 
side  of  the  eye  toward  the  nose.  At  the  point  where  the 
nerve  leaves  the  eye  there  is  a  small  area  which,  having  no  rods 
or  cones  and  no  pigment  (these  structures  alone  are  really 
sensitive  to  light),  is  blind  and  is  therefore  called  the  blind 
Spot.  In  the  ordinary  use  of  the  eyes,  however,  we  do  not 
notice  the  presence  of  any  such  area. 

EFFECT  OF  LIGHT  IN  THE  EYE 

How  does  light  act  on  the  parts  of  the  eye  which  are  sen- 
sitive to  it — the  pigment  and  the  rod  and  cone  layers  of  thej 
retina?     No  one  has  any  precise  knowledge  of  this  matter,] 
but  there  are  two  interesting  theories  as  to  its  effect. 

The  Chemical  Theory. — The  chemical  theory  supposes  thai 
the  chemical  composition  of  the  pigment  layer  is  changed  by] 
light,  somewhat  as  is  the  sensitive  plate  in  a  camera  whenj 
ilie  abutter  is  opened.     The  theory  rests  upon  these  facts :j 


ORGANS  OF  SPECIAL  SENSE— THE  EYE  357 

(1)  that  the  amount  of  pigment  increases  when  the  eye  is 
closed,  and  decreases  when  Hght  enters  it;  (2)  that  if  the  eye 
of  an  animal  be  closed,  the  animal  then  immediately  killed 
and  the  eye  first  opened  in  a  solution  of  alum  in  a  dark  room, 
the  image  of  the  last  thing  seen  by  the  eye  can  thus  be  pre- 
served in  the  pigment  layer.  (Such  a  picture  is  called  an 
optogram).  A  difficulty  in  the  way  of  accepting  this  theory 
is  that  it  supposes  the  pigment  to  be  constantly  broken  down 
by  light  and  again  restored.  In  reading,  for  example,  the 
shapes  of  thousands  of  letters  and  the  spaces  between  them 
and  between  the  lines  are  continually  appearing  and  forming 
rapidly  changing  pictures  on  the  retina.  In  the  ordinary  use 
of  the  eyes,  hundreds  of  different  images  are  being  formed  and 
changed  every  minute.  In  order  to  be  continually  in  con- 
dition to  receive  new  light  rays,  i.e.  receive  new  images,  the 
pigment  would  have  to  undergo  repairs  at  a  rate  of  which  we 
can  hardly  conceive. 

The  Mechanical  Theory. — The  mechanical  theory  supposes 
that  light  falling  on  the  retina  disturbs  or  shakes  the  rods  and 
cones,  and  thus  starts  in  them  impulses  which  travel 
through  their  connections  to  the  optic  nerve  and  thence  go 
to  the  brain.  How  can  this  be  possible?  In  answering  this 
question  we  have  to  remember  that  light  itself  is  in  the  form 
of  very  short,  wave-like  movements.  The  rapidity  of  these 
vibrations  is  almost  beyond  our  powers  of  appreciation;  but 
the  theory  is  that  they  pass  into  the  eye  and  thus  stir  the  rods 
and  cones  to  the  same  rapid  movement,  the  disturbance 
being  interpreted  in  the  brain  as  *'Ught." 

The  main  reason  for  doubting  that  the  effect  of  light  in  the 
eye  is  so  simple  is  that  the  light  waves  take  place  at  such  very 
rapid  rates.  For  instance,'  the  slowest  movements  which  we 
interpret  as  hght  at  all  occur  at  the  rate  of  107,000,000,000,000 
per  second;  the  fastest  rate  which  we  can  perceive  at  all  is 
40,000,000,000,000,000  per  second.  Red  hght  vibrates  at 
392,000,000,000,000,   and  violet  at  757,000,000,000,000  per 


358  ADVANCED  PHYSIOLOGY 

second;  the  other  colors  which  we  can  see  are  caused  by 
vibrations  at  rates  between  those  of  red  and  violet.  Although 
these  figures  really  mean  very  little  to  us,  it  is  certainly  im- 
probable that  the  material  particles  which  we  call  rods  and 
cones  can  be  thrown  into  such  rapid  movement,  and  especially 
hard  is  it  to  see  how  their  rates  of  vibration  could  be  changed 
from  one  frequency  to  another  with  such  accuracy  as  they 
must  be  when  one  suddenly  looks  from  red  to  violet,  or  from 
yellow  to  green,  for  example. 

In  spite  of  the  reasons  which  make  it  seem  hard  to  believe 
the  action  of  light  on  the  retina  of  the  eye  to  be  either  chemical 
or  mechanical,  we  can  hardly  avoid  the  conclusion  that  it 
must  be  one  of  these  two,  or  a  combination  of  them.  We  are 
practically  forced  to  say  that  we  do  not  know  what  light 
really  does  in  the  eye. 

COLOR  VISION  AND  COLOR  BLINDNESS 

We  have  already  noted  that  in  the  back  of  the  eye  cones 
are  especially  abundant  and  diminish  toward  the  sides  of  the 
retinal  area,  while  rods  are  few  at  the  back  and  plenty  on  the 
sides.  Hence  light  entering  the  eye  from  the  side  would 
strike  mainly  on  rods,  while  that  going  straight  toward  the 
back  would  disturb  chiefly  cones.'  If  we  keep  this  fact  in 
mind,  and  reflect  that  the  color  of  an  object  is  most  plainly 
seen  when  the  object  is  straight  in  front  of  us,  we  must  con- 
clude that  the  cones  are  the  more  sensitive  of  the  two  to  color 
changes.  Rods  seem  to  be  sensitive  to  light  and  shade,  but 
not  to  color,  while  cones  are  sensitive  to  both.  It  can  be 
proved  by  experiment,  too,  that  a  larger  area  of  the  retina 
is  sensitive  to  one  color  than  to  another;  for  example,  one  can 
see  violet  objects  as  they  are  brought  around  slowly  from  the 
side  to  the  front  sooner  than  he  can  identify  a  green  object  so 
brought  before  him.  Consequently  we  conclude  that  the  area 
of  the  eye  which  can  see  violet  is  larger  than  that  which  can 
perceive  green.     The  area  which  can  see  red  is  also  larger  than 


ORGANS  OF  SPECIAL  SENSE— THE  EYE  359 

that  which  is  sensitive  to  green,  but  smaller  than  that  which  is 
sensitive  to  violet.  Physiologists  claim  that  red,  green  and 
violet  are  the  only  colors  perceived  by  the  eye,  and  that  other 
colors  are  seen  when  two  or  more  of  these  colors  are  stimulated 
at  the  same  time,  in  different  degrees. 

Color  blindness  is  a  more  common  defect  than  is  supposed. 
It  consists  in  inability  to  see  any  difference  between  two 
colors  which  seem  to  most  people  very  unlike  and  distinct. 
The  most  common  kind  is  that  in  which  a  person  is  unable  to 

I  distinguish  between  red  and  green.  To  such  a  person  the 
only  difference  between  red  apples  and  green  leaves  on  the 
same  tree  would  be  merely  a  difference  in  shape  and  brightness. 
If  one  accepts  the  theory  that  the  eye  perceives  only  red, 
green  and  violet,  then  red  color  blindness  would  be  explained 
by  supposing  that  the  red  sensations  were  only  imperfectly 
developed,  or  perhaps  altogether  lacking. 

Persons  who  are  colcfr  blind  cannot  obtain  employment  on 
railroads  or  ships,  for  in  such  positions  it  is  absolutely  neces- 
sary that  one  see  clearly  both  red  and  green,  since  flags, 
lights  etc.,  used  as  signals  are  generally  of  these  colors. 
There  is  no  known  remedy  for  this  defect. 

CARE  OF  THE  EYES 

Probably  no  defects  are  so  apt  to  escape  attention  and 
proper  treatment  as  imperfections  in  the  eyes.  Even  in 
cases  where  the  eye  is  very  defective,  one  may  see  fairly  well 
and  so  neglect  to  attend  to  the  matter.  The  result  is  that 
some  part  of  the  eye  may  be  in  a  condition  of  strain,  trying  to 
force  the  refractive  surfaces  into  shape  to  produce  a  proper 
focus  upon  the  retina.  This  strain  brings  on  fatigue  of  the 
delicate  muscles  themselves  and  exhaustion  of  the  nerves 
that  may  lead  to  serious  results,  e.  g.  headaches,  indigestion, 
nausea  and  various  nervous  diseases.  Any  one  of  these  out- 
comes is  sufficient  practically  to  disable  a  person  for  hard 
work  and  to  cloud  living  with  continuous  pain.     The  mental 


380  ADVANCED  PHYSIOLOGY 

and  physical  disturbances  which  follow  in  the  wake  of  eye 
defects  should  lead  one  to  the  most  jealous  care  of  these 
priceless  organs.  Glasses  should  be  fitted  by  a  skillful 
oculist  as  soon  as  it  is  discovered  that  the  eyes  are  unable 
easily  to  meet  the  demands  upon  them.  The  cost  of  this 
sort  of  care  should  not  be  allowed  to  influence  one  in  the  matter 
of  procuring  and  following  the  most  expert  advice. 

If  one  has  to  hold  a  book  nearer  to  the  eye  than  12  inches, 
the  indication  is  that  he  is  nearsighted.  On  the  other  hana, 
if  he  finds  it  necessary  to  hold  a  book  20  inches  or  more  from 
the  eyes  to  read  it  easily,  the  probability  is  that  he  is  farsighted. 
In  either  case  he  should  consult  an  occuUst. 

Some  troubles  due  to  imperfect  eyes,  such  as  headaches 
and  nervousness,  are  not  always  recognized  as  associated 
with  those  organs.  Sometimes  a  child  in  school  is  thought 
stupid  when  the  trouble  is  that  he  cannot  see  what  is  written 
on  the  blackboard.  A  wise  plan  has  been  adopted  in  many 
schools  in  recent  years,  undei*  which  the  eyes  of  each  scholar 
are  tested  to  determine  whether  or  not  he  needs  glasses. 
Properly  adjusted  glasses  not  only  bring  relief  to  strained 
eyes  but  so  improve  general  health  that  everyone  ought  to 
welcome  an  examination  of  his  eyes,  and  if  necessary  the 
adoption  of  proper  glasses. 

In  ordinary  life,  through  ignorance  and  carelessness  we 
frequently  use  our  eyes  unwisely  and  in  such  a  way  as  to 
invite  or  increase  a  tendency  to  eye  trouble.  A  few  general 
suggestions,  therefore,  may  be  profitably  remembered  by 
everyone. 

Illumination. — By  changes  in  the  size  of  the  pupil  consider- 
able variation  in  intensity  of  illumination  can  be  met,  since 
the  pupil  opens  in  dim  light  and  closes  in  bright.  Too  dim 
light,  as  for  instance  that  at  twilight,  taxes  the  eyes  severely 
if  one  tries  to  use  them  for  exacting  work,  like  reading.  On 
the  other  hand,  very  bright  light  is  equally  injurious,  so  that 
one  should  not  allow  sunlight  to  fall  upon  a  page  he  is  reading. 


ORGANS  OF  SPECIAL  SENSE-THE  EYE  361 

Flickering  Light. — A  light  whose  intensity  is  constantly 
changing  is  very  tiresome.  It  is  injurious  to  read  by  candle- 
light, not  so  much  because  it  is  dim,  as  because  it  is  not 
steady.  Reading  in  the  cars  is  very  taxing  because  the  im- 
ages on  the  retina  are  those  of  an  object  which  is  constantly 
shaken  by  the  motion  of  the  car. 

Resting  the  Eyes. — Eyes  are  made  for  use  and  if  properly 
treated  will  grow  stronger,  but  if  overtaxed  they  will 
suffer  quickly.  Reading  fine  print  or  looking  intently  and 
constantly  at  small  objects  is  always  severe  on  the  eyes. 
Everyone  whose  work  requires  such  application  should 
appreciate  the  need  of  giving  the  eyes  an  occasional  rest  by 
looking  off  at  distant  objects,  or  by  ceasing  to  use  them  at  all. 
If  rested  in  this  way  xhey  may  be  used  for  exacting  work  for 
years  without  injury. 

Injuries. — The  eyes  are  too  delicate  to  be  carelessly  treated 
and  injuries  to  them  usually  need  the  attention  of  a  physician. 
A  particle  of  dust  or  a  cinder  in  one's  eye  can  usually  be  re- 
moved with  ease,  however.  In  most  cases  tears  will  quickly 
wash  it  over  the  surface  to  the  tear  duct.  This  process  may 
be  assisted  by  seizing  the  lids  with  the  fingers  and  lifting  them 
away  from  the  eyeball,  when  the  tears  that  accumulate  will 
ordinarily  dispose  of  the  dust.  The  eye  should  not  be  rubbed. 
If  the  dust  particle  is  under  the  lower  lid,  this  can  easily  be 
lifted  and  the  particles  be  removed  on  the  corner  of  a  hand- 
kerchief; if  it  is  under  the  upper  lid,  this  can  be  rolled  up 
gently  over  a  lead  pencil.  A  physician  should,  however,  take 
care  of  any  serious  eye  trouble. 


CHAPTER  XXII 

THE  EAR 

Although  externally  the  ear  does  not  appear  to  be  so 
delicate  an  organ  as  the  eye,  yet  as  a  sense  organ  it  is  scarcely 
less  iiiiricate  m  structure,  or  necessary  in  daily  life.  It  has 
been  noted  that  the  eye  is  quite  protected  in  its  rather  deep 
socket;  but  the  ear  is  yet  more  secure,  being  set  deeply  into 
and  almost  surrounded  by  the  temporal  bone  of  the  cranium. 
For  convenience  in  description  it  is  treated  as  though  in  three 
parts,  the  outer,  the  middle,  and  the  inner  ear. 

The  Outer  Ear. — The  portion  of  the  ear  which  protrudes 
on  the  side  of  the  head  is  made  up  largely  of  skin,  containing 
several  small  pieces  of  cartilage  which  give  it  shape.  In  many 
animals  the  outer  ear  is  large  and  acts  as  an  organ  for  gathering 
sound  waves  and  leading  them  against  the  ear  drum  inside; 
in  man,  however,  this  use  of  the  outer  ear  is  practically  gone, 
and  it  has  no  special  function.  Muscles  for  moving  it,  which 
are  highly  developed  in  many  and  especially  in  four-footed 
animals,  are  present  in  man  also,  but  have  degenerated 
through  lack  of  use.  The  old-fashioned  ear  trumpet  was 
merely  an  auxiliary  contrivance  for  collecting  more  sound 
waves  and  conducting  them  into  the  ear. 

The  canal  leading  into  the  head  is  called  the  external 
auditory  meatus;  Fig.  181.  This  comes  to  an  abrupt  ending 
against  a  thin  membrane,  the  ear  drum,  or  tympanic  mem- 
brane. The  canal  dips  downward  a  little  as  it  goes  inward, 
and  this  fact  explains  how  it  is  that  water  may  get  into  the 
ear  when  one  has  the  head  under  water  when  swimming,  and 
why  it  can  only  be  gotten  out  by  tipping  the  head  to  one  side 

362 


I 


THE  EAR 


363 


and  j  arring  it.  In  the  skin  which  lines  this  canal  are  numerous 
glands  that  secrete  a  substance  which  partially  evaporates 
and  leaves  what  is  called  ear  wax.  This  seems  to  have  little 
function,  but  it  should  never  be  interfered  with  except  by  a 
competent  physician. 

The  Middle  Ear. — The  middle  ear  is  a  space  just  inside  the 
ear  drum  (Fig.  181)  and  is  scientifically  called  the  tym- 
panum. The  cavity 
is  not  large  and  is 
surrounded  by  bone 
on  all  sides  save  at 
a  few  points,  which 
will  be  especially 
noticed  later.  On  the 
lower  side  of  this  cav- 
ity is  an  opening  lead- 
ing into  the  Eusta- 
chian tube,  which 
passes  down  to  the 
throat.    On  the  inner 

the  inner  ear  is  shown  natural  size.      In  the  upper      sidQ  of  the  tvmpaUUm 
figure  the  external  ear  is  shown  much  too  small 


Fig.  181. — Diagram 

Showing  the  structure  of  the  ear.  In  the  lower  figure 


relatively  to  the  size  of  the  internal  structures. 
The  oblique  shading  represents  bone.  A,  external 
meatus;  B,  utricle;  C,  saccule;  D,  semi-circular 
canal;  £^,  nerve;  i^,  cochlea;  G,  Eustachian  tube; 
H,  tympanic  membrane;  /,  cochlea. 


are  two  small  open- 
ings, which  lead  to  the 
inner 'ear,  but  which 
are  closed  by  mem- 
branes; the  upper  one  is  the  foramen  ovale,  the  lower, 
the  foramen  rotimdum.  At  the  upper  part  of  the  tympanum 
are  some  minute  pores  leading  into  spaces,  called  the  mastoid 
cavities,  in  the  surrounding  bone.  Reaching  across  the  tym- 
panic cavity  is  a  chain  of  three  httle  bones;  Fig.  181. 

The  Eustachian  Tube. — The  Eustachian  tube  serves  two 
very  important  functions.  First,  it  allows  air  to  go  in  and 
out,  between  the  ear  and  the  pharynx.  At  first  thought  it 
seems  odd  that  there  should  be  any  connection  between  the 
ear  and  the  throat,  but  such  connection  is  necessary  to  keep 


364  ADVANCED  PHYSIOLOGY 

the  air  in  the  middle  ear  at  the  same  pressure  as  that  outside, 
so  that  the  ear  drum  may  be  kept  flat.  The  Eustachian  tube 
is,  therefore,  of  especial  use  in  enabling  one  to  adapt  himself 
to  different  altitudes.  At  the  sea-level,  atmospheric  pressure 
is  much  greater  than  on  the  tops  of  mountains;  if  the  Eu- 
stachian tube  did  not  thus  regulate  internal  pressure  in  the  ear, 
the  drum  would  sometimes  be  pressed  inward  or  again  out- 
ward, perhaps  to  the  breaking  point.  The  Eustachian  tube 
is  also  useful  as  a  drainage  way  for  the  middle  ear;  its  lining  is 
ciliated,  and  mucus  which  is  formed  in  small  quantities  in  the 
tympanum  is  thus  carried  to  the  pharynx. 

The  Eustachian  tube  is  not  generally  open;  it  is  rather  in 
the  condition  of  a  thin  rubber  tube,  with  its  sides  collapsed. 
Its  closing  prevents  the  voice,  which  is  produced  in  the  voice 
box  just  below  the  opening  of  the  tube  into  the  pharynx,  from 
passing  up  the  tube  and  creating  a  loud  disturbance  during 
ordinary  conversation.  Moreover,  if  the  tube  were  con- 
stantly open,  air  would  be  continually  passing  in  and  out  of 
the  middle  ear  as  one  breathes.  This  would  keep  the  thin 
membrane  of  the  drum  and  the  partition  between  the  middle 
and  inner  ear  cavities  under  constantly  changing  pressures, 
and  irritate  the  hearing  organ  seriously. 

Mastoid  Cavities. — Whether  or  not  the  mastoid  cavities  are 
of  any  value  is  not  clear;  but  they  are  sometimes  the  cause  of 
serious  trouble.  When  there  is  inflammation  in  this  region 
and  the  cavities  become  filled  with  pus,  producing  a  disease 
called  mastoiditis,  the  most  skilled  physician  or  surgeon 
should  be  given  charge  of  the  case.  The  distance  from  the 
mastoid  region  to  the  brain  is  so  short  that  inflammation  can 
easily  spread  through  the  thin,  bony  walls  of  the  brain  cavity, 
and  if  the  brain  becomes  involved  the  trouble  may  be  fatal. 

The  Ear  Bones. — There  are  three  tiny  bones  stretching  in 
a  zigzag  course  across  the  middle  ear  cavity,  from  the  ear 
drum  to  the  foramen  ovale;  Fig.  182.  The  first  is  the  malleus 
(hammer),  and  is  fastened  to  the  drum  at  one  end.     From 


THE  EAR 


365 


Jncus 


tlalleus 


there  it  extends  upward,  where  it  is  attached  to  the  second 
bone,  the  incus.  This  bone  has  something  the  shape  of  a 
blacksmith's  anvil  (hence  the  name  incus)  and  one  projection 
from  it  extends  downward  into  the  cavity  again,  connecting 
with  the  third  bone,  the  stapes  (stirrup),  which  ends  in  a  broad, 
flat  area,  fitting  into  the 
opening  mentioned  above 
as  the  foramen  ovale;  Fig. 
182.  """'^^^iiis^   7"'W/-i    /^^^ 

The  three  bones  are  con- 
nected by  ligaments,  and 
there  is  practically  no 
hinge  action  except  be- 
tween the  incus  and 
stapes.  Two  tiny  muscles 
are  connected  with  these 
bones;  one,  the  tensor  tym- 
pani,  leads  from  the  wall  of 
the  Eustachian  tube  to  the 
malleus  bone.  When  it 
shortens,  it  pulls  on  the 
malleus  and  thus  indirectly 
tightens  the  drum.  The  other  muscle,  the  stapedius,  runs 
from  the  wall  of  the  cavity  to  the  neck  of  the  stapes,  and 
when  it  contracts  pulls  the  stapes  to  one  side,  thus  changing 
the  position  of  the  membrane  over  the  foramen  ovale.  The 
value  of  these  muscles  will  be  discussed  later. 

The  Inner  Ear. — The  foramen  ovale  is  a  short  passage  in 
the  bone  and  leads  into  a  series  of  cavities  which  constitute 
the  inner  ear.  As  shown  in  Figure  181,  this  cavity  is  com- 
plicated and  difficult  to  understand.  Altogether  it  is  no 
larger  than  the  end  joint  of  the  Uttle  finger,  but  it  is  the  loca- 
tion of  the  whole  organ  of  hearing  and  of  balancing.  Inside 
the  foramen  ovale  membrane  is  a  cavity  called  the  vestibule, 
filled  with  a  thin  watery  fluid,  the  perilymph.     The  cavity  ia 


Tqmpamc  tJembrane 

Fig.  182. — The  ear  bones 
Stretching  across  the  middle  ear  from  the 
tympanic  membrane  to  the  foramen  orvale. 
(Hensen) 


366 


ADVANCED  PHYSIOLOGY 


not  a  simple  one,  but  from  its  main  central  portion  (Fig.  181) 
three  tubes  lead  out  into  the  surrounding  bone  in  different 
directions,  make  half  circle  turns  and  come  around  into  the 
central  cavity  again.  On  the  posterior  side  of  this  cavity  a 
longer  canal,  twisted  into  a  spiral  form,  goes  out  into  the  bone. 
In  this  curiously  shaped  cavity  and  floating  in  its  fluid  are 
two  thin-walled  sacs;  the  larger  is  called  the  utricle  and  is 
connected  with  the  smaller,  the  saccule,  by  a  slender  canal. 
From  the  utricle  membranous  tubes,  called  the  semicircular 
canals,  run  through  the  three  half  circular  canals  noted  above. 
Extending  from  the  other  sac,  i.e.  the  saccule,  and  following 
the  course  of  the  spix-al  tube  in  the  bone,  is  another  mem- 
branous canal.  This  spiral  bony  canal  and  its  contained 
membranous  canal  are  together  called  the  cochlea.  The 
utricle,  the  saccule  and  all  the  tubes  in  connection  with  them 
are  filled  with  a  clear,  watery  fluid,  the  endolymph. 

FUNCTION  OF  THE  SEMICIRCULAR  CANALS 


■Posterior  Semicircular  Canal 
.-External  » »  " 


Superior^ 


Cochlea 


'Saccule 
Utricle 


The  ear  is  usually  thought  of 
as  an  organ  of  hearing  rather 
than  one  of  balancing,  but  the 
semicircular  canals  are  con- 
cerned with  the  latter  function. 
Figure  182A  shows  that  each 
canal  has  a  swelling,  an  am- 
pulla, at  one  end  near  where  it 
leaves  the  utricle.  The  inner 
structure  of  an  ampulla  is 
shown  in  Figure  183. 
On  one  side  of  the  ampulla  is  a  ridge,  and  on  top  of  the 
ridge  are  a  number  of  hair-Uke  projections,  among  which  are 
lime  granules.  The  direction  in  which  the  canals  run  should 
also  be  noted.  No  two  pass  around  through  the  bone  in  the 
same  plane;  one  lies  approximately  in  a  horizontal  plane, 
another  in  a  vertical  plane,  in  a  right-to-left  direction,  and  the 


Ampulla 
Fig.  182  A.     Diagram 

OF  BAR   PARTS 


THE  EAR 


367 


third  in  a  vertical  plane,  in  a  front-to-back  direction.  Thus, 
one  of  these  canals  is  located  in  each  of  the  three  planes  of 
space,  in  each  of  the  maia  directions  in  which  the  body  can  be 
inclined. 

If  the  location  and  structure  of  the  canals  is  clear,  their 
manner  of  functioning  can  be  readily  understood.  They  are 
filled  with  endolymph,  and  when  the  head  is  rotated,  this 
fluid  acts  as  water  does  in  a  pail  or  glass  jar  when  the  latter 
is    turned  around  in 

the  hands.  The  liquid  lime,  qranules 

scarcely  moves,  but 
the  pail  or  jar  slips 
around  outside  the 
liquid.  If  there  were 
threads  attached  to 
the  sides  of  the  pail, 
these  would  be  bent 
back  and  forth  by  the 
water  slipping  over 
them  as  the  pail  was 
turned  first  one  way 
and  then  the  other;  in 

like  manner,  if  the  head  is  tipped  from  side  to  side,  or  forward 
and  backward,  the  endolymph  in  the  canals  tends  to  stay  in  its 
original  position,  while  the  canals  slip  around  it.  This  makes 
the  hair-like  projections  on  the  crests  in  the  ampullae  bend  to 
and  fro,  and  since  nerve  fibres  end  in  these  ampullae,  this  sway- 
ing of  the  threads  creates  a  message  which  is  carried  to  the 
brain.  In  tipping  in  any  direction,  the  lime  granules  will  set- 
tle on  different  parts  of  the  ampullae.  This  will  irritate 
nerves  ending  in  these  regions,  and  the  result  is  that  one  has 
a  sensation  of  inclining  from  side  to  side,  of  falling  or  of  rolling 
over,  as  the  case  may  be. 

Of  course  all  the  movements  one  makes  are  not  in  the  exact 
planes  in  which  the  semicircular  canals  lie,  but  they  are  at 


Fig. 183. — ^^A  section  of  one  of  the  ampulla 

OF  THE  SEMI-CIRCULAR  CANALS   (Kolliker) 


368  ADVANCED  PHYSIOLOGY 

least  somewhere  between  them,  in  which  case  the  endolymph 
in  two  of  the  canals  is  moved,  and  from  the  resulting  sensation 
one  judges  the  direction  of  the  body  motion.  These  facts,  too, 
explain  why  children  who  have  been  whirling  about  on  their 
feet  in  one  direction  for  some  time  become  dizzy.  If  a  pail 
of  water  is  whirled  long  enough  in  one  direction  the  water 
will  finally  get  to  whirHng  with  the  pail;  and  if  then  the  pail 
is  suddenly  stopped  the  water  will  keep  on  moving  for  some 
time.  In  the  same  way,  a  whirling  child  sets  the  endolymph 
moving  in  the  direction  in  which  the  canals  go,  so  that  the 
latter  no  longer  slip  around  outside  the  endolymph;  when  the 
child  stops  whirling  the  endolymph  keeps  on  moving  in  the 
canals,  and  though  the  body  is  quite  erect,  messages  continue 
to  go  to  the  brain,  and  the  resulting  sensation  makes  the  nerve 
center  feel  that  some  other  position  of  the  body  must  be  sought. 
Messages  are  consequently  sent  out  to  some  muscles  to  relax 
and  to  others  to  contract.  As  a  result  the  child  makes  stagger- 
ing movements,  or  falls  over.  Relief  can  be  obtained  quickly 
by  whirling  in  the  opposite  direction  for  a  moment,  thus  com- 
pelling the  endolymph  to  overcome  more  friction  and  sooner 
become  quiet. 

THE  STRUCTURE  AND  FUNCTION  OF  THE  COCHLEA 

The  shape  of  the  cochlea  tube,  as  it  winds  into  the  bone  of 
this  region,  has  already  been  described  as  that  of  a  spiraL 
The  diagram  in  Figure  184,  which  represents  the  cochlea  as 
unwound  and  straightened  out,  makes  this  matter  of  the  con- 
nection between  the  cochlea  and  vestibule  clear.     The  part  of j 
the  structure  "which  has  to  do  with  hearing  is  the  dottec 
horizontal  tube,  in  the  walls  of  which  the  auditory  nerves 
end.     The  cochlea  is  large  where  it  leaves  the  vestibule,  but] 
grows  smaller  as  it  coils.     It  has  often  been  likened  to  aj 
snail's  shell,  and  indeed  takes  its  name  from  that  fact. 

Extending  through  the  membranous  tube  (marked  cochlea! 
in  Figure  184)  is  a  pecuUar  organ,  a  sketch  of  which  (highly! 


THE  EAR 


369 


4 


magnified)  is  shown  in  Figure  185.  This  is  called  the  organ 
of  Corti,  and  in  it  are  the  endings  of  the  auditory  nerve  fibres. 
It  is  the  real  organ  of  hearing,  just  as  the  retina  is  the  organ 
of  sight.  The  manner 

in  which  it  is  affected  .,/^.  ^^i^..     .VesHbule 

by  sound  is  not  fully 
known,  but  it  is  prob- 
ably    something     as 

ollows : — 
Sound  is  produced 

y  vibrations  or  waves 
of  the  air.  When 
waves  reach  the  body 
they   pass    into    the 


Coc  hleo  UincoHed) 


Fig.  184. — Diagram 

Showing  the  relation  of  the  cochlea   (uncoiled)   tc 

the  vestibule  and  other  parts  of  the  ear. 


external  auditory  meatus  until  they  come  against  the  tympanic 
membrane  or  drum.  As  the  waves  fall  upon  this  they  set  it  to 
moving  at  the  rate  at  which  they  strike  it.  This  movement  of 
the  drum  will  evidently  be  transmitted  to  the  ear  bones  attached 


Haircelh 


Fig.  185. — Section  of  the  organ  of  corti 

Highly  magnified.     Showing  the  real  hearing  part  of  the  ear.  (Retzius) 


to  it  and  by  their  motion  the  end  of  the  stapes  is  pulled  back 
and  forth  in  the  foramen  ovale.  This  motion  will  in  turn 
produce  a  similar  set  of  little  waves  in  the  liquids  of  the  in- 
ternal ear,  with  the  result  that  the  whole  mass  of  liquid  will 
vibrate  just  as  rapidly  as  the  air  outside  the  head.     As  a  re- 


370  ADVANCED  PHYSIOLOGY 

suit,  the  organ  of  Corti,  which  Hes  quite  freely  in  the  Hquid, 
will  also  be  thrown  into  vibration.  In  this  organ,  as  we 
have  learned,  are  the  ends  of  the  nerves  of  hearing,  and  it  is 
supposed  that  the  slight  shaking  they  thus  receive  is  sufficient 
to  stimulate  them  so  that  they  transmit  impulses  to  the  brain, 
which  are  then  interpreted  as  sound. 

Perception  of  Pitch. — The  method  by  which  the  ear  recog- 
nizes high  and  low  tones  is  not  fully  understood,  but  it  ap- 
pears to  be  in  part  based  upon  a  very  simple  fact.  Sound  is 
the  result  of  air  waves,  and  the  different  pitches  are  due  to 
waves  of  different  degrees  of  rapidity.  In  high  sounds  the 
rate  is  very  rapid,  in  low  sounds  it  is  slow;  the  longest  strings 
of  a  piano  vibrate  about  thirty-three  times  per  second,  the 
shortest  strings  about  four  thousand  two  hundred  times.  If 
one  stands  close  to  a  piano  and  plays  a  loud  note  upon  a  flute, 
for  example,  and  then  stops,  he  will  notice  that  he  can  hear 
the  same  note  sounding  in  the  piano  for  several  seconds. 
The  waves  of  air  starting  from  the  flute  have  passed  into  the 
piano  and  strike  upon  the  various  strings.  There  is  one 
string  in  the  instrument  that  naturally  vibrates  just  as 
rapidly  as  the  waves  which  come  from  the  flute,  and  these 
wave  motions  from  the  flute  set  that  particular  wire  into 
vibration,  so  that  even  after  the  flute  is  silent,  one  can  hear  a 
faint  sound  from  the  piano  string.  If  two  notes  were  played 
near  the  piano  at  the  same  time,  two  wires  would  be  set  into 
vibration,  etc.  This  phenomenon  takes  place  according  to 
a  principle  known  as  that  of  sympathetic  vibration. 

By  reference  to  Fig.  185  it  is  noted  that  the  rods  of  Corti  and 
the  ^'hair  cells"  seem  to  stand  on  a  straight,  basal  membrane; 
this  is  really  a  shelf-like  curtain  which  is  attached  to  the  core 
of  the  spiral  cochlea  along  one  edge,  and  to  the  outer  curve  of 
the  tube  on  the  other,  dividing  it  into  two  spaces  lengthwise. 
This  basilar  membrane  is  made  up  of  about  24,000  threads 
(Retzius)  of  practically  as  many  lengths.  These  basilar  mem-  j 
brane   threads,    it   is    thought,    vibrate    at    different   rates, 


THE  EAK  an 

much  as  do  the  various  wires  of  a  piano.  When,  therefore, 
the  liquids  in  the  inner  ear  are  thrown  into  vibration,  it  is 
evident  that  some  part  of  the  organ  of  Corti  will  naturally 
vibrate  with  exactly  the  same  rapidity  as  the  movements  of 
the  liquid,  according  to  the  laws  of  sympathetic  vibration. 
Thus  for  every  different  sound  a  nerve  fibre  will  be  stimulated, 
and  the  brain  recognizes  the  different  pitches.  While  this 
general  theory  of  tone  perception  seems  to  be  reasonable  and 
correct,  we  must  admit  that  as  yet  no  one  knows  precisely 
what  part  the  organ  of  Corti  plays  in  the  appreciation  of 
sounds. 

Loudness  of  Sound. — Loudness  of  sound  depends,  not  on 
the  rate  at  which  air  is  moving  in  waves,  but  on  the  size  of 
the  waves;  not  on  the  rapidity  of  vibrations,  but  on  their 
amount.  This  we  know  from  the  simple  fact  that  a  piano 
string  struck  heavily  will  give  out  a  loud  sound;  if  struck 
gently,  a  low  sound,  though  of  the  same  pitch  as  when  struck 
heavily.  Violent  movements  in  the  air  are  set  up  when  the 
string  is  vibrating  back  and  forth  through  considerable  dis- 
tance after  being  struck  hard,  and  these  start  large  waves 
in  the  surrounding  air,  which  however  vibrate  at  the  same 
rate  as  if  the  wire  had  been  struck  gently.  These  violent 
movements  are  finally  transferred  to  the  inner  ear  over  paths 
we  have  already  discussed,  and  thus  the  nerve  endings  in  the 
organ  of  Corti  are  greatly  irritated.  One  interprets  this 
strong  stimulation  as  loudness  of  sound;  faint  sounds  are  con- 
versely due  to  very  slight  air  waves  and  slight  nerve  stimula- 
tion. 

When  listening  intently  to  catch  some  faint  sound,  almost 
everyone  strikes  the  same  instinctive  attitude.  The  body  is 
held  very  quietly,  the  ear  turned  in  the  direction  from  which 
the  sound  is  expected,  and  the  whole  attention  is  focused  on 
the  ear.  In  the  perception  of  faint  sounds,  slight  changes 
occur  in  the  middle  ear,  and  the  purpose  of  these  changes  may 
be  understood  from  the  analogous  action  of  a  drumhead. 


372  ADVANCED  PHYSIOLOGY 

When  a  drum  head  is  loosely  drawn,  the  drum  will  sound 
very  well  if  struck  hard  enough  with  the  sticks,  but  if 
the  drummer  merely  touches  the  head  or  hits  it  very  gently, 
no  sound  of  consequence  comes  from  it.  If,  on  the  other  hand, 
the  drum  head  is  drawn  tight  by  shoving  down  the  straps  on 
the  cords  at  the  sides  of  the  drum,  the  merest  movement  of 
the  sticks  on  the  head  produces  a  very  distinct  noise. 

In  the  middle  ear  the  two  tiny  muscles,  mentioned  on 
page  365,  are  so  placed  that  they  can  tighten  the  membranes 
bordering  on  the  middle  ear,  so  that  the  least  movement  of 
sound  waves  in  the  air  can  be  detected.  The  tensor  tympani 
draws  the  ear  drum  tight,  and  the  stapedius  pulls  on  the  stapes 
and  adjusts  the  membrane  over  the  foramen  ovale;  the 
ear  is  thus  put  into  condition  for  perceiving  very  faint  sounds 

Quality  of  Sound. — As  has  already  been  pointed  out,  the 
quality  of  one's  voice  is  determined  not  entirely  by  the  nature 
of  the  vocal  cords,  but  by  the  size  and  shape  of  the  cavities  of 
the  trachea,  the  pharynx,  the  nose  and  some  smaller  cavities 
in  the  bones  of  the  upper  part  of  the  nose.  The  air  in  these 
cavities  is  set  in  vibration  by  sound  waves,  and  the  people 
who  are  listening  to  one's  voice  get  the  effect  of  all  the  inci- 
dental influences  of  the  cavities  upon  the  sound.  How 
marked  the  influence  of  these  centers  is  may  be  proved  by 
merely  closing  the  nasal  passages — grasping  the  nose  between 
the  fingers  while  talking. 

DEAFIiESS 

Defective  hearing  is  due  to  a  variety  of  circumstances.  In 
elderly  people  it  is  generally  caused  by  the  stiffening  of  the 
ear  drum  or  other  delicate  membranes  so  that  they  are  not 
so  sensitive  to  slight  sound  waves  as  formerly,  or  it  may  be 
due  to  the  fact  that  the  bones  of  the  middle  ear  have  become 
more  or  less  rigid  and  do  not  move  readily. 

In  younger  people,  and  in  those  who  become  temporarily 
deaf,  the  trouble  usually  is  that  the  Eustachian  tubes  have 


« 


THE  EAR  373 

become  closed  by  some  inflammation  of  the  tissues  about  them. 
This  often  happens  to  a  person  who  has  catarrhal  troubles. 
A  bad  "sore  throat"  may  produce  deafness  or  '^ringing 
sounds"  in  the  head  for  this  simple  reason.  The  result  of 
the  closure  of  the  Eustachian  tubes  is  that  the  pressure  of  air 
in  the  tympanic  cavity,  or  middle  ear,  becomes  different  from 
that  outside  (whether  greater  or  less,  the  result  is  the  same) 
and  the  membranes  involved  will  not  act  well  under  these 
strained  conditions.  Such  circumstances  impose  a  kind  of 
stress  on  the  fluids  of  the  inner  ear,  so  that  they  can  move 
very  little,  if  at  all.  ''Ringing  noises"  may  be  due  to  the 
fact  that  the  fluids  cannot  move  in  the  normal  way,  and  these 
being  under  extra  stress,  a  large  proportion  of  the  nerve  end- 
ings in  the  ear  feel  the  strain,  and  innumerable  mild  messages 
go  to  the  hearing  center  in  the  brain.  These  may  be  so  con- 
tinuous and  disturbing  as  to  induce  headaches  and  generally 
disagreeable  results.  One  should  not  allow  the  trouble  to 
continue  long  without  submitting  it  to  skilled  treatment.  If 
a  ''buzzing  in  the  ears''  or  temporary  deafness  occurs  as  the 
result  of  a  cold,  a  physician  should  be  consulted,  since  such 
troubles,  left  unattended,  may  result  in  permanent  deafness. 
The  other  so-called  special  senses  are  taste,  smell  and  the 
sense  of  feeling,  including  touch,  heat  and  cold.  Each  of 
these  has  been  considered  in  previous  chapters  and  need  not 
be  discussed  here. 


CHAPTER  XXIII 
THE  CONTROL  OF  HEALTH 

Personal  Hygiene. — As  one's  usefulness  in  the  world 
depends  directly  on  the  quantity  and  quality  of  mental  and 
physical  energy  he  has  to  spend,  it  is  necessary  to  know  the 
important  factors  which  contribute  to  personal  health  and 
efficiency  such  as  in  food,  exercise,  sleep,  etc.  We  cannot 
exercise  too  great  care  in  the  selection,  preparation  and  eating 
of  our  food,  or  we  shall  yet  condemn  ourselves  to  ill-health  by 
our  unwisdom. 

Foods. — Our  food  should  be  selected  with  reference  to  a 
proper  balance  of  elements  as  outlined  in  Chapter  III.  Pro- 
teids,  carbohydrates,  and  fats  are  all  vitally  necessary,  as  well 
as  certain  constituents  (vitamines)  found  in  vegetables  and 
milk.  The  action  of  vitamines  is  not  yet  thoroughly  under- 
stood, but  it  is  known  they  play  a  very  important  role. 

Excess  of  any  food  qualities  to  the  exclusion  of  others  will 
finally, though  not  immediately, reduce  the  body  to  weakness; 
this  must  never  be  forgotten. 

Constipation,  or  the  failure  of  food  materials  to  be  steadily 
carried  through  the  digestive  tube,  results  in  abnormal  decom- 
position and  the  formation  of  poisons  which,  absorbed,  cir- 
culate through  and  injure  the  whole  body.  This  condition 
can  be  avoided  in  most  cases  (a)  by  the  use  of  coarse  breads, 
bran,  graham,  and  the  like;  (6)  by  the  use  of  leafy  vegetables, 
the  larger  part  of  which  are  never  absorbed  but  become  a 
"roughage"  which,  in  contact  with  the  intestinal  wall,  pro- 
vokes peristalsis;  (c)  by  the  right  use  of  fats  and  oils;  (d)  by 
the  use  of  fruits.     The  old  saying,  **An apple  a  day  keeps  the 

374 


THE   CONTROL  OF  HEALTH  375 

doctor  away",  may  be  taken  seriously,  (e)  Temporary  laxa- 
tives, such  as  drugs,  must  not  be  employed  frequently,  or  the 
system  will  come  to  depend  upon  them.  Paraffin  oil  (Amer- 
ican oil)  is  one  of  the  safest  and  best  laxatives  and  is  not 
unpleasant  to  the  taste.  (/)  By  the  use  of  plenty  of  water. 
Two  quarts  per  day  is  not  too  much  for  a  person  weighing 
150  pounds.  Water  taken  in  Hquid  foods  is  needed  in  addition 
to  this  amount,  (g)  Exercise,  by  which  the  body  is  repeatedly 
bent  into  various  positions,  subjects  the  abdominal  organs  to 
various  pressures,  the  nerves  are  awakened,  and  the  blood 
flow  quickened. 

Salt  and  condiments :  The  fact  that  salt  (NaC)  leaves  the 
body  in  the  same  form  as  it  enters  makes  it  no  less  a  necessity. 
In  1000  parts  of  blood  there  are  5.5  parts  of  salt.  Its  intimate 
role  in  the  body  is  not  entirely  understood.  Spices  have  no 
food  value,  and  should  as  a  rule  be  eaten  sparingly.  Flavors 
make  foods  more  palatable,  and  in  themselves  are  generally 
harmless. 

Beverages:  Coffee  and  tea  are  the  commonest  table  bever- 
ages exclusive  of  water.  In  using  them  one  must  remember 
that  their  food  value  is  nil,  save  for  the  cream  and  sugar 
usually  taken  with  them.  Caffein,  in  coffee,  excites  certain 
nerve  centres,  and  hastens  kidney  excretion,  necessitating 
abnormal  demands  on  the  organs  involved.  Thein,  an 
ingredient  in  tea,  seems  to  prevent  free  digestive  action  of 
saliva  on  starch.  The  use  of  either  tea  or  coffee  cannot  be 
commended,  and  must  be  strictly  limited.  Cocoa  and  choco- 
late have  decided  food  value,  but  contain  also  theo-bromine 
which  has  the  same  properties  in  general  as  caffein. 

The  so-called  **soft  drinks,"  soda  waters,  etc.,  may  have 
small  sugar  value,  but  as  generally  taken,  interfere  with  the 
appetite  for  wholesome  food,  and  besides  the  purchase  of  them 
is  a  waste  of  money. 

Irregular  Eating. — The  habit  of  eating  between  meals  is  a 
specially  vicious  one  if  the  regular  meals  are  the  proper  time 


376  ADVANCED  PHYSIOLOGY 

*  apart,  and  are  adequate  for  the  kind  of  work  being  done. 
If  one  feels  faint  or  nauseated  before  a  meal,  the  probability 
is  that  his  last  meal  was  deficient  and  a  lunch  would  have  been 
very  wisely  taken.  The  stomach,  digestive  organs  and  glands 
must  be  given  rest,  just  as  we  know  muscles  and  nerves 
demand  it.  The  appetite  may  suggest  irregular  and  frequent 
eating,  but  its  suggestions  may  not  always  be  followed.  See 
page  51. 

Alcoholic  Beverages.  ^ — ^The  effect  of  alcoholic  beverages 
upon  the  nervous  system  has  already  been  discussed. 

Exercise.  —  Muscles  comprise  fully  40  %of  the  body  weight, 
and  their  condition,  healthful  or  otherwise,  affects  the  body 
as  a  whole.  The  blood,  going  to  and  from  every  tissue, 
carries  away  materials  from  muscle  of  a  nature  unlike  that 
taken  from  any  other  part  of  the  body.  As  the  blood  stream 
hurries  on,  every  other  tissue,  e.  g.  nerves,  glands,  etc.,  is 
influenced  by  what  has  gone  into  the  blood  stream  from 
muscles. 

These  changes  which  take  place  when  a  resting  muscle 
begins  to  act  are  as  follows:  (a)  Sarco-lactic  acid  is  produced 
and  replaces  the  alkaline  character  of  resting  muscle.  (6) 
Loosely  combined  oxygen  is  speedily  associated  with  carbon 
forming  CO2.  (c)  Glycogen  already  stored  in  the  muscle  is 
transformed  and  poured  into  the  blood  as  dextrose,  (d)  The 
temperature  of  the  muscle  is  raised. 

These  changes,  happening  in  the  muscle  itself,  are,  through 
the  blood  stream,  felt  throughout  the  body,  with  many  accom- 
panying results,  some  of  which  are:  (a)  The  respiration  is 
quickened  and  as  a  result  the  air  is  rapidly  changed  in  the 
lung  recesses  and  the  respiratory  muscles  are  exercised  and 
given  new  **tone."  (6)  The  heart  beats  faster,  all  blood  tubeS' 
are  thus  flushed  and  their  own  muscular  walls  called  into 
action,  (c)  The  mechanism  which  regulates  the  temperature 
of  the  whole  body  is  roused  and  put  to  work,  (d)  Blood  and 
lymph  are  forced  away  from  points  where  they  may  have 


THE   CONTROL   OF  HEALTH  377 

become  sluggish  in  their  flow,  (e)  The  digestive  system 
receives  a  reflex  stimulus  and  is  much  benefited. 

Exercise  which  comes  through  physical  work  directed  to 
some  useful,  productive  end,  brings  its  most  genuine  and 
cheerful  satisfaction.  Play  differs  from  most  work  in  its 
excess  of  mental  exhilaration,  its  spirit  of  winning,  its  call  for 
particular  skill,  its  social  companionship.  Exercise,  to  be  of 
value,  should  be  vigorous,  though  not  to  the  point  of  strain; 
it  should  call  for  repeated  moderate  action  of  the  same  set  of 
muscles  rather  than  a  few  severe  or  sustained  contractions. 
Gymnasia  offer  opport»unities  for  varied  exercises  which  have 
been  selected  with  the  advice  of  trained  directors  to  meet  the 
individual  need  for  the  correction  of  faulty  physique. 

Sleep.  —  Sleep  is  the  great  restorer  of  the  nervous  system. 
One  should  sleep  with  wide-open  windows  or  in  sleeping 
porches.  The  hygienic  reasons  for  sleep  are  these :  (a)  Every 
other  system  of  organs  except  the  nervous  system  can  secure 
rebuilding  during  waking  hours,  if  it  is  deliberately  excused 
from  action;  but  unconsciousness  is  the  only  condition  which 
permits  nerves  to  *'let  go."  (b)  Sleep  gives  the  time  necessary 
for  the  more  complete  elimination  of  wastes.  A  thorough 
freeing  from  katabolic  products  cannot  occur  while  new  ones 
are  constantly  added  to  those  in  the  blood  and  lymph.  This 
purification  can,  however,  be  largely  accomplished  in  eight 
consecutive  hours  of  total  inactivity  in  sleep,  (c)  Sleep 
permits  that  relaxation  which  cannot  occur  when  one  is  active 
mentally.  A  kind  of  tone  or  tension  pervades  the  entire 
system  normally  when  awake  and  this  needs  to  be  excluded 
regularly. 

Hygiene  of  Particular  Organs:  Eyes. — No  organ  of  the 
entire  body  is  more  intricate  than  the  eye.  Its  defects,  if 
any,  have  a  far  reaching  influence  on  other  organs,  e.  g., 
serious  digestive  irregularities,  headache  and  nervousness 
often  result  from  eye-strain.  If  these  symptoms  are  present, 
or  if  it  is  difficult  to  see  objects  clearly  unless  held  very  near 


378  ADVANCED   PHYSIOLOGY 

(6  or  8  inches)  or  very  far  away,  or  if  the  image  of  the  object 
is  blurred  in  any  way  whatever,  a  skilled  ocuUst  should  be 
consulted  to  remedy  the  defect.  When  reading  book  or  paper 
of  average  sized  type,  it  should  not  be  held  nearer  the  eye  than 
sixteen  inches;  nor  should  the  focussing  muscles  be  obliged  to 
act  for  that  distance  for  long  periods  without  rest.  To  obtain 
a  change  in  the  focussing  requirement  when  reading,  look 
about  the  room  or  out  of  the  window  occasionally. 

Too  intense  light  is  apt  to  be  used.  It  is  only  by  actual 
strain  that  the  eye  can  function  in  our  customary  brilUant 
illumination  and  if  a  gUstening  paper  or  picture  is  being 
examined  the  result  is  all  the  worse. 

Ears. — To  preserve  good  hearing,  nothing  must  interfere 
with  any  portion  of  the  hearing  apparatus.  No  small  object 
should  be  allowed  to  touch  the  ear-drum,  much  less  puncture 
it.  Ear  *Vax"  should  be  removed  with  much  care,  and  not 
permitted  to  collect. 

The  greatest  danger  to  the  ear  lies  in  its  relation,  via  the 
Eustachian  tube,  to  the  throat.  Inflammation  of  the  pharynx 
can  thus  spread  to  the  middle  ear,  and  cause  pus  formation 
either  there  or  in  the  nearby  mastoid  cells  (page  364) .  It  is 
difficult  to  cure  such  a  condition  without  endangering  the 
hearing  function. 

Social  Hygiene. — By  this  term  is  meant  the  relation  which 
the  mingling  of  people  in  numbers  has  upon  the  health  of 
each  one,  and  of  all  collectively.  In  a  general  way,  the 
health  of  a  community  is  the  sum  total  of  the  health  of  its 
individuals. 

Ever  since  the  germ  theory  of  disease  was  established  by 
Pasteur,  it  has  been  well  known  that  the  health  of  a  home  or 
the  health  of  a  whole  community  may  be  determined  by  the 
health  or  the  sickness  of  a  single  individual.  The  process  of 
the  transfer  of  a  disease  from  one  person  to  another  is  termed 
a  process  of  infection. 

Infection.  —  Quite  a  contrast  with  the  days  of  long  ago. 


THE  CONTROL  OF  HEALTH  379 

we  now  know  that  many  diseases  are  definitely  passed  from 
one  person  to  another  either  (1)  by  contact,  or  (2)  by  taking 
into  the  body  * 'particles'*  given  off  from  the  body  of  the  sick 
individual.  Other  diseases  are  caused  by  the  body  being 
invaded  by  certain  of  the  lower  animals  (e.  g.  malarial  organism, 
trichina),  or  by  bacteria. 

* 'Contagious**  and  ''infectious'*  diseases  are  now  considered 
essentially  identical,  being  communicable.  Among  these 
are  typhoid  fever,  cholera,  measles,  mumps,  whooping  cough, 
smallpox,  —  communicable  from  man  to  man.  From  the 
lower  animals  man  "catches'*  tuberculosis,  anthrax  (splenic 
fever)  from  cattle,  malta  fever  from  goats,  malaria  from 
mosquitoes,  plague  from  rats,  and  tapeworms  from  various 
meats. 

The  main  problem  in  avoidance  of  disease  concerns  those 
which,  in  bacterial  form,  are  passed  from  man  to  man.  These 
organisms  secure  an  entrance  generally  in  one  of  three  ways: 
(1)  in  the  food  we  eat;  (2)  in  the  air  we  breathe;  (3)  by  way 
of  the  skin,  through  natural  pores  or  through  injured  surfaces. 

Two  fundamental  facts  of  bacteriology  must  be  kept  in 
mind ;  bacteria  thrive  either  when  in  moist  substances  or  when 
dry  or  semi-dry  so  that  they  may  float  in  the  air,  either  free, 
or  attached  to  dust.  Dust  blows  about  and  settles  every- 
where, e.  g.  on  clothing,  hands  and  face,  on  solid  and  liquid 
foods  if  exposed,  eating  and  cooking  utensils,  furniture  of  all 
sorts,  curtains  and  floor  coverings.  These  are  mentioned 
that  we  may  not  forget  what  may  be  sources  of  bacterial 
infection,  and  how  thoroughly  all  the  articles  in  a  room  with 
a  sick  person  may  be  the  lodging  places  of  disease  bacteria. 
Such  articles  as  are  nearest  him  are  most  liable  to  carry  them, 
e.  g.  personal  clothing,  bedding,  handkerchiefs,  knives,  forks, 
spoons,  dishes,  and  all  containers  of  waste  material. 

After  handling  such  articles  as  these  just  mentioned,  if  one 
is  to  safely  guard  against  infection,  the  hands  should  be 
thoroughly   disinfected  by  using   germ-killing   washes,  such 


380  Advanced  I'hysiology 

as  2%  carbolic  acid  solution,  or  a  very  weak  (0.1%)  solution 
of  corrosive  sublimate.  Some  of  the  germ-laden  dust  from 
clothing  or  bedding  may  have  been  breathed  in,  and  an 
antiseptic  solution  should  be  used  as  a  mouth  wash  and 
gargle,  as  well  as  nasal  spray. 

As  a  rule,  washes  for  the  skin  should  never  be  used  for 
mouth  or  nasal  disinfection. 

Recently  opinion  has  inclined  to  the  belief  that  many 
diseases  are  spread  by  the  droplet  method;  e.g.  when  the 
patient,  or  carrier  of  the  disease  germs,  coughs,  sneezes,  or 
even  talks,  he  expels  into  the  air  minute  droplets  of  the 
mucuous  fluids  of  the  mouth  or  near-by  breathing  passages. 
These  droplets  float  about  in  the  air  and  may  be  breathed  in, 
or  fall  on  utensils  or  foods  which  may  later  be  put  into  the 
mouth,  and  thus  the  well  person  be  infected  by  the  bacteria 
which  are  in  these  droplets. 

Any  person  who  is  ill,  even  with  a  cold,  should  never  fail 
to  use  a  handkerchief  over  the  nose  and  mouth  when  coughing 
or  sneezing  and  should  never  face  toward  a  nearby  person 
when  talking,  laughing,singing,  or  the  like. 

The  period  of  time  which  usually  elapses  between  infection 
and  the  actual  on-coming  of  the  disease  (called  the  incubation 
period)  varies  much  even  with  exposures  to  the  same  disease. 
This  is  because  the  body  is  in  better  physiological  condition 
at  one  time  than  another,  or,  in  other  words,  possesses  more 
resistance.  Persons  differ  greatly  in  their  susceptibility  to 
disease  and  some  may  even  be  immune  while  others  are  very 
liable  to  a  given  disease.  The  following  table  is  given  to 
indicate  the  time  during  which  a  person,  knowing  of  his 
exposure  to  some  disease,  should  avoid  close  association  with 
others : 

Small-pox 14  days 

Measles 10    " 

Scarlet  fever 3     " 

Diphtheria 3    " 


THE  CONTROL  OF  HEALTH  381 

Chicken-pox 20  days 

Whooping  cough 21     " 

Cholera 10    " 

Typhoid  fever     ........        14    " 

Mumps 24    ** 

Infantile  Paralysis 28    " 

Immunity. — In  a  previous  chapter  (page  72)  we  have 
defined  immunity  as  a  condition  of  the  body  such  that  it  is 
not  susceptible  to  a  communicable  disease  even  when  inti- 
mately exposed  to  it.  For  example,  the  same  mosquito 
(genus  Anopheles,  and  carrying  malarial  germs)  biting  a  man 
and  a  bird,  conveys  malarial  fever  to  the  man  but  not  to  the 
bird.  Another  genus  of  mosquito  (Culex)  biting  both,  causes 
malaria  in  the  bird  but  not  in  man.  Each  organism  is  naturally 
immune  to  the  bacteria  which  cause  a  disease  in  the  other. 

Immunity  cannot  in  any  way  be  secured  against  some 
maladies,  e.  g.  tuberculosis.  Immunity  is  being  secured 
against  an  increasing  number  of  diseases  by  artificial  and 
harmless  means.  The  discoveries  made  by  Louis  Pasteur 
marked  what  may  justly  be  considered  the  most  important 
epoch  in  the  history  of  medicine,  and  what  may  almost  be 
called  the  physical  salvation  of  mankind. 

To  understand  how  immunity  may  be  brought  about 
requires  attention  to  the  relation  which  exists  between  the 
invading  bacteria  and  the  person  invaded. 

When  disease  bacteria  from  any  source  obtain  entrance  to 
the  human  body,  they  soon  become  vigorous  and  multiply 
very  rapidly  because  of  the  warm  temperature  and  of  the 
nutrition  they  so  easily  absorb  from  the  body  fluids.  Under 
favorable  circumstances  a  single  bacterium  of  certain  kinds 
may  give  rise  to  as  many  as  17,000,000  descendants  in  twenty- 
four  hours.  Passing  from  the  respiratory  or  digestive  organs 
into  the  blood  or  lymph,  they  give  from  their  bodies  substances 
called  toxins,  which  are  often  very  poisonous, and  cause  the 
discomfort  and  symptoms  of  th^  (disease.  /  The  cells  of  the 


382  ADVANCED   PHYSIOLOGY 

body  (probably  those  of  the  blood  vessels  in  particular)  being 
irritated  by  these  toxins,  endeavor  to  defend  themselves  by 
giving  off  materials  which  nullify  the  poisons.  These  sub- 
stances are  called  antitoxins.  If  the  body  cells  can  create 
sufficient  antitoxin  rapidly  enough,  the  bacteria  as  well  as  their 
products  are  overcome,  and  the  person  will  soon  be  well  again. 
It  is  quite  obvious  that  the  blood  of  a  person  so  recovering 
contains  antitoxin  substances  which  will  make  him  safe  from 
similar  attack  so  long  as  they  last.  He  is  then  said  to  be 
actively  immune  to  that  special  disease. 

One  may  secure  immunity  against  some  diseases  by  means 
other  than  first  going  through  a  period  of  sickness  with  it. 
The  commoner  means  are  by  vaccination  and  by  serum 
inoculations  or  injections.  The  principle  on  which  both  these 
procedures  work  is  this:  if,  instead  of  virile  disease  bacteria, 
very  weak  (attenuated)  germs,  or  the  toxin  secreted  by  them, 
are  introduced  into  the  human  body  through  a  shallow  abrasure 
or  cut  in  the  skin  (vaccination)  or  by  hypodermic  injection 
(injection  or  innoculation) ,  enough  antitoxin  is  immediately 
produced  by  the  body  so  that  the  weak  germs  are  killed  off 
and  the  toxin  made  of  no  effect.  With  antitoxin  thus  on 
hand,  the  body  has  a  * 'running  start"  and  can  successfully 
compete  against  the  invasions  of  strong,  vicious  bacteria  of 
the  same  sort.  This  is  the  manner  of  procedure  against 
typhoid  and  small-pox.  The  wide  use  of  vaccination  for 
small-pox  and  innoculation  for  typhoid  fever  has  thoroughly 
established  their  reliability  and  safety.  Persons  so  rendered 
safe  from  a  certain  disease  are  said  to  be  artificially  immune. 

Instead  of  injecting  weak  and  dying  bacteria  or  the  toxin 
characteristic  of  them,  the  body  can  be  fortified  against  some 
diseases  by  injecting  antitoxin  taken  from  some  animal  which 
has  had  the  disease  and  recovered  from  it;  this  is  the  case 
when  serums  are  injected  to  ward  off  diphtheria.  Curiously 
enough,  the  body  cells  can  be  deceived  in  this  way,  and  on 
becoming  * 'conscious"  of  the  presence  of  some  antitoxin  will 


THE   CONTROL  OF   HEALTH  38?. 

busily  begin  to  make  more  like  it.  A  quantity  is  thus  soon 
on  hand  sufficient  to  combat  successfully  the  heaviest  infections. 

Home  and  School  Hygiene.  —  Since  at  least  one  half  the 
life  of  each  person  is  spent  indoors,  it  is  very  essential  that 
homes,  school  buildings,  etc.,  should  be  as  conducive  as  pos- 
sible to  the  health  and  general  welfare  of  mind  and  body. 
Many  matters  of  building  hygiene  apply  equally  to  dwellings 
and  school-houses,  so,  unless  specially  designated,  the  following 
considerations  pertain  to  both. 

Primarily  a  home  should  be  located  with  reference  to  its 
water  suppljs  drainage,  air  supply,  and  light.  Beauty  of 
surroundings,  freedom  from  noise,  relation  to  markets  and 
transportation  conveniences,  and  congeniality  of  neighbors 
are  likewise  considerations  of  real  importance. 

Location  and  Water  Supply.  —  Wherever  one  is,  he  cannot 
live  unless  provided  with  pure  water  in  unfaihng  quantity. 
If  wells  are  the  only  source  of  water,  they  must  be  carefully 
isolated  from  contamination  by  house  or  barn  drainage. 
A  knowledge  of  **the  lay  of  the  land"  where  the  well  is  dug 
should  be  obtained  so  that  underlying  layers  of  rock  or  imper- 
vious earth  (clay)  may  not  lead  impure  water  into  the  well 
from  a  distance.  The  area  immediately  about  such  a  well 
should  be  raised  decidedly  above  the  general  level,  and 
cemented  over  for  a  distance  of  at  least  six  feet  on  all  sides 
of  the  opening,  to  prevent  rains  from  washing  surface  debris 
either  directly  or  indirectly  into  the  well.  It  should  be 
covered  tightly  to  prevent  leaves,  dust,  foreign  matter,  or 
small  animals  from  getting  into  the  water. 

If  one  is  contemplating  living  in  any  given  city  or  village, 
the  source  of  its  water  supply,  its  treatment,  the  manner  of 
its  storage  and  method  of  delivery  should  be  investigated. 
No  portion  of  a  water-shed  affecting  a  supply  should  be  a  place 
of  human  habitation  unless  all  the  circumstances  of  such  a 
house  are  known,  and  its  drainage  prohibited  from  entering 
the  waters  destined  for  household  use. 


384  ADVANCED  PHYSIOLOGY 

In  case  a  town  supply  must  be  taken  from  a  river,  pond, 
or  lake,  the  science  of  sterilizing,  softening  and  clearing  water 
is  so  highly  developed  there  is  no  reason  why  wholesome 
waters  should  not  be  secured.  Clearness,  ''softness,"  and  lack 
of  odor  do  not  insure  pure  water.  Its  bacterial  content  is 
of  more  significance  than  any  other  single  factor;  and  the 
number  of  bacteria  is  of  little  consequence  as  compared  with 
their  kind.  Bacteria  which  thrive  in  decomposing  organic 
material  should  not  be  present,  particularly  such  as  are  found 
in  the  human  digestive  canal.  If  such  are  found,  it  is  obvious 
that  insanitary  drainage  from  human  dwellings  is  somehow 
entering  the  supply,  and  the  health  of  every  person  using  this 
water  is  in  imminent  danger. 

The  temperature,  except  for  affecting  its  palatableness,  has 
nothing  to  do  with  its  desirableness.  If  ice  is  used  in  water, 
one  should  be  certain  that  it,  in  turn,  is  made  from  pure  water, 
and  in  its  use  one  should  remember  the  physiological  fact  that 
cold  temporarily  slows  or  even  stops  the  action  of  life  pro- 
cesses. 

Location  and  Drainage. ^ — Formerly,  if  the  basement  of  a 
house  kept  dry,  little  was  thought  of  other  drainage.  The 
water  wastes  were  thrown  on  the  near-by  ground,  and  either 
allowed  to  sink  in,  or  to  run  into  an  open  ditch.  Solid  matters 
were  allowed  to  collect  wherever  they  might. 

In  modern  times,  large  amounts  of  water  are  used  in  washing, 
rinsing,  house-cleaning,  and  the  like.  Lavatories,  bathtubs, 
and  the  sanitary  water-flushed  toilet  have  become  necessities 
of  civilization.  Rainwater  should  be  conducted  away  and 
not  be  allowed  to  fall  from  the  eaves,  as  this  undermines  the 
foundations  and  creates  a  damp,  unwholesome  basement. 

Houses  should  be  so  located  that  all  waste  water  can  be 
conducted  away  to  a  safe  distance;  in  order  to  do  this  the 
house  should  stand  above  the  general  level  so  this  drainage 
may  be  easily  and  surely  secured. 

House  Construction.^ — A  dry  basement  is  very  essential. 


THE   CONTROL  OF   HEALTH  385 

It  is  secured  by  keeping  surface  water  away  from  foundation 
walls  by  tight  bottom  construction,  and  by  a  drainage  exit 
for  any  water  which  may  enter  in  unanticipated  ways. 

The  side  walls  of  a  building  are  much  warmer  if  made  in  at 
least  two  thicknesses  (preferably  three)  with  an  air  space 
between.  This  same  method  of  insulation  against  a  tempera- 
ture change  is  used  in  the  construction  of  refrigerators  and 
incubators,  where  maximum  uniformity  in  temperature  is 
wanted.  Windows  should  be  numerous,  both  for  purposes  of 
light  entrance  and  for  ventilation.  The  doors  as  well  as  the 
windows  should  be  fitted  with  screens  so  that  insects  may  be 
kept  out,  as  some  of  these  are  now  well  known  carriers  of 
numerous  kinds  of  disease  * 'germs"  (bacteria). 

Walls  and  floors  of  rooms  should  be  so  finished  as  to  be 
easily  kept  free  from  dirt  and  dust.  Fancy  wood-work  in 
which  dust  collects  and  which  is  cleaned  with  difficulty,  is 
unhygienic. 

Location  with  Reference  to  Light  and  Air.  —  Whether 
in  city  or  country,  one  should  keep  in  mind  the  need  of  adequate 
hght  and  the  vital  necessity  of  plenty  of  pure  air  when  deciding 
on  a  place  of  residence.  Dense  shade  from  trees  or  an  environ- 
ment of  high  buildings  makes  the  eyes  work  under  difficulties, 
necessitates  the  expense  of  artificial  light,  and  constitutes  a 
condition  of  general  unwholesomeness.  This  is  because  sun- 
light is  one  of  the  most  effective  agents  in  the  destruction  of 
bacteria.  Sunny  rooms  are  not  merely  well  lighted,  but  are 
healthful.  This  germicidal  action  of  light  should  be  utiUzed 
by  putting  clothing,  rugs,  and  house-furnishings  in  the  open 
air  on  sunny  days. 

Artificial  Light. — Of  the  modern  methods  of  artificial 
lighting,  electricity  is  by  far  the  most  convenient  and  hygienic. 
Its  convenience  is  obvious,  and  its  use  is  hygienic  because 
there  is  no  leakage  or  odor  as  with  gas  or  oil  lighting.  Electric 
lighting  systems  have  now  been  developed  so  that  a  home  in 
the  country  may  be  lighted  by  electricity. 


386  ADVANCED   PHYSIOLOGY 

Tn  the  use  of  gas,  care  should  be  taken  to  prevent  an^^ 
leakage,  to  adjust  the  mixture  of  gas  and  air  at  each  burner, 
so  as  to  obtain  the  most  light,  and  to  obviate  vitiating  the  air 
with  unoxidized  gas. 

Acetylene  gas  plants  are  often  placed  in  private  houses, 
especially  in  the  country;  here  again  leakage  should  be  par- 
ticularly guarded  against,  and  users  should  clearly  understand 
its  explosive  qualities.  Kerosene  oil  may  be  burned  where 
other  artificial  illumination  is  not  available,  but  extreme 
cleanliness  is  necessary  to  prevent  bad  odors  and  to  secure 
maximum  light. 

In  all  kinds  of  illumination,  our  tendency  is  to  employ  too 
brilliant  Hght  and  to  use  too  little  care  in  preventing  light 
from  shining  or  being  reflected  directly  into  the  eyes.  From 
whatever  source,  light  should  come  from  over  the  shoulder, 
not  from  the  front  or  side. 

Artificial  Heat.- — Stoves  are  still  used  for  heating  houses, 
even  though  they  are  somewhat  unsatisfactory  for  this  pur- 
pose. They  are  unsatisfactory  for  several  reasons:  Dust  and 
dirt  accumulate  about  them;  the  distribution  of  the  heat  in 
the  room  is  uneven;  the  floors  remain  cold  above  the  basement; 
poisonous  gases  may  escape  (from  coal  stoves) ;  and  the  danger 
of  fires  from  a  number  of  stoves  in  one  house  is  increased. 
Central  heating  from  a  furnace  obviates  all  these  objections. 
Each  of  the  different  sorts  of  central  heating  systems,  hot  air, 
steam  and  hot  water,  has  points  in  its  favor  as  well  as  against  it. 

Hot  Air  Furnace:  The  hot  air  system  brings  fresh  air  into 
the  house,  at  such  temperatures  as  to  obviate  cold  drafts, 
and  in  this  respect  is  a  most  desirable  method  of  heating; 
but  dust  is  almost  certain  to  collect  in  the  furnace  and  delivery 
pipes,  and  be  brought  up  in  the  air  current.  As  winds  greatly 
modify  the  dehvery  of  hot  air  to  different  rooms  in  the  house, 
the  equable  distribution  of  the  hot  air  on  cold,  windy  days 
is  not  always  possible. 

Steam  System:  In  this  system,  the  steam  pressure  can  be 


THE  CONTROl.  OF  HEALTH  387 

raised  to  such  a  degree  that  the  radiators  can  be  made  very 
hot  in  severe  weather  and  every  room  thoroughly  warmed. 
The  objections  to  steam  heat  are:  The  air  of  a  room  is  heated 
over  and  over  with  no  ventilation  unless  such  is  specially 
provided;  the  radiators  may  become  over-hot  and  "burn  up" 
the  air;  and  no  heat  is  obtained  from  the  fire  till  the  water  is 
near  the  boiling  point. 

Hot  Water  System:  This  has  the  advantage  of  delivering 
some  heat  to  the  radiators  as  soon  as  the  water  is  slightly 
warm.  The  heat  is  steady,  and  the  radiators  remain  warm  a 
long  time  after  the  fire  is  low.  The  disadvantages  of  this 
heating  plan  are  that  the  radiators  never  get  so  warm  as  with 
steam,  and  must  therefore  be  much  larger  for  the  same  service; 
furthermore,  ventilation  must  be  secured  in  ways  not  related 
to  the  heating  system. 

Ventilation.  • — ■  Ventilation  is  necessary  for  several  reasons : 
breathed  air  contains  too  little  oxygen,  too  much  CO2,  too 
much  moisture  and  too  many  organic  compounds  in  small 
amounts.  Each  person  vitiates  about  1,800  cubic  feet  of 
air  per  hour,  and  provision  must  be  made  for  its  renewal  or  the 
individual  becomes  inefficient  in  working  power  and  in  resis- 
tance to  disease,  and  is  reduced  to  poor  health  generally. 

Of  all  the  many  ways  of  letting  fresh  air  into  rooms,  the 
old-time  method  by  way  of  windows  and  doors  is  one  of  "the 
best;  forced  ventilation  with  flues  and  fans  is  seldom  entirely 
satisfactory  and  is  very  expensive.  A  good  way  to  ventilate 
a  room  is  to  let  fresh  air  enter  near  the  top  of  the  room,  and  to 
let  the  stale  air  escape  at  the  bottom  as  through  a  fireplace  or 
some  similar  exit.  Fresh  air  is  bound  to  enter  around  loose 
windows  and  doors. 

Especial  provision  must  be  made  for  all  buildings  where 
many  people  congregate  as  in  schools,  churches,  and  theatres. 
Sufficient  air  space  cannot  be  secured  for  such  rooms  unless 
they  are  made  very  large,  or  with  high  ceilings.  No  drafts, 
either  warm  or  cold,  should  be  allowed  during  cold  weather; 


388  ADVANCED   PHYSIOLCC'A' 

temperature  should  not  vary  more  than  2°  from  68°  F.,  and 
the  air  should  be  neither  too  dry  nor  too  moist.  In  buildings 
heated  with  steam  or  hot  water,  special  consideration  should 
be  given  the  matter  of  humidity,  as  very  dry  air  is  irritating  to 
the  lung  membranes  and  is  thus  a  menace  to  health.  Moisture 
should  be  provided  in  the  form  of  steam,  and  the  supply 
regulated  by  an  automatic  humidometer. 

Furnishings.  ~  Whatever  the  use  of  the  building,  its  fur- 
nishings must  be  such  as  may  easily  be  kept  clean.  Fancy 
wood  furniture  or  iron  desks  are  kept  free  from  dust  with  great 
difficulty.  Carpets  fastened  down  so  that  dirt  cannot  be 
removed  from  under  them  are  now  little  used;  only  such  rugs 
as  can  be  easily  and  thoroughly  cleaned  should  be  considered 
practical  or  desirable.  Window  hangings  and  upholstery 
should  also  be  selected  primarily  with  reference  to  healthful- 
ness. 

Cleaning  of  Buildings.  —  In  performing  any  cleaning  the 
one  prime  rule  to  insist  upon  is  NO  DUST,  whatever  the 
method  used.  If  the  dust  is  removed  and  not  scattered  in 
the  process,  the  method  is  excellent.  Cloths  used  in  dusting 
should  be  oiled  to  entangle  and  remove  dust,  not  scatter  it  as 
was  the  case  with  the  old-fashioned  feather  duster.  Prepara- 
tions for  entangling  the  dust  and  dirt  should  be  scattered  on 
floors  before  sweeping  them,  and  unless  a  vacuum  cleaner  is 
used,  rugs  should  be  taken  out  of  doors  to  be  cisaned. 

In  school-houses  chalk  dust  should  be  wiped  from  black- 
boards with  a  damp  cloth  or  some  other  dust  absorber.  The 
chalk  trough  below  the  board  should  be  covered  with  wire 
screening  to  keep  hands  and  erasers  from  the  dust.  Slate 
boards  are  cleaner  than  wooden  ones,  besides  largely  doing 
away  with  the  glare  from  reflected  light. 

Disinfection  of  Rooms  and  their  Contents.  — •  This  pro- 
cedure as  a  preventive  against  the  spread  of  disease  is  of  very 
much  less  value  than  was  once  supposed.  For  instance,  there 
seems  very  little  virtue  in  disinfection  after  cases  of  measles. 


THE   CONTROL  OF   HEALTH  389 

whooping  cough,  influenza,  pneumonia,  diphtheria,  or  men- 
ingitis. 

Clothing  and  bedding  which  may  have  been  stained  by 
fluids  from  the  body  of  a  sick  person  should  be  thoroughly 
boiled  and  other  articles  from  the  sick  room  hung  in  the  air 
and  sunshine  for  several  hours  to  free  them  from  bacteria. 
Thin  clothing  hanging  in  a  closet  can  be  disinfected  by  placing 
a  small  sheet,  sprayed  with  strong  formalin,  in  the  closet  and 
closing  the  door  tightly  for  some  hours. 

If  a  room  is  to  be  disinfected,  the  permanganate-formalin 
method  is  considered  the  best.  The  method  of  procedure  is 
as  follows:  After  sealing  the  room  air-tight  (strips  of  paper 
can  be  pasted  over  cracks),  place  potassium  permanganate 
(250  grams^ — 9  ounces  for  each  100  cubic  feet  of  space)  in  a 
very  deep  pail  near  the  middle  of  the  room;  the  pail  should 
stand  on  a  couple  of  bricks  or  similar  support  as  the  bottom 
will  become  hot.  When  all  is  ready,  pour  onto  the  perman- 
ganate 500  cc.  (about  1  pint)  of  formalin,  full  strength.  The 
gas  from  this  has  poor  penetrating  power,  so  that  thick  cloth- 
ing, bedding,  etc.,  should  be  given  special  treatment,  i.  e. 
steamed,  boiled  or  soaked  in  5%  solution  of  formahn. 

Special  Home  Problems:  Sewage  Disposal.  ^ — In  most 
municipalities  refuse  from  kitchen  sinks,  lavatories,  and 
toilets  is  carried  away  by  the  sewage  system.  In  smaller 
villages  and  country  places,  private  cess-pools,  with  un- 
cemented  walls  will,  with  little  attention,  take  care  of  the 
needs  of  an  ordinary  house  for  some  years.  Such  a  cess-pool 
must  never  be  located  so  that  seepage  from  it  will  enter  any 
supply  of  water. 

In  the  country,  if  privy  vaults  are  necessary,  they  should 

be  perfectly  isolated  from  flies  or  vermin  and  be  so  closed  and 

treated  as  to  be  free  from  odor.     The  container  should  be  a 

I      removable,  water-tight  can,  the  contents  of  which  should  be 

I      frequently  buried,  never  thrown  on  top  of  the  ground. 

IK    Special      School    Problems:     {a)     Sanitation     of     Public 


S90  ADVAisrCED  1>HYSI0L0GY 

Buildings.- — -Schools,  theatres,  and  churches  are  the  com- 
monest meeting  places  of  the  people  of  a  neighborhood. 
These  meetings  afford  an  ideal  opportunity  for  the  spread  of 
disease.  Close  personal  contact  is  almost  inevitable,  rebreath- 
ing  of  air  is  certain,  common  water  faucets  and  toilets  are  the 
rule. 

The  proper  management  of  a  schoolhouse  or  any  other 
pubhc  building  is  one  of  its  greatest  educational  influences, 
as  its  sanitary  arrangements  and  general  cleanliness  will  no 
doubt  affect  those  benefited  by  them. 

Too  great  emphasis  cannot  be  laid  on  the  importance  of 
extreme  sanitation  in  school  lavatories  and  toilets.  Any  part 
of  the  equipment  of  these  rooms  which  has  been  touched  by 
the  diseased  surface  of  a  person  suffering  from  a  communicable 
disease  is  very  hable  to  be  a  source  from  which  the  disease 
may  be  transferred  to  others. 

Drinking  fountains,  paper  towels,  and  laws  compelling  the 
use  of  only  new  books  are  among  the  most  recent  developments 
of  sanitary  science. 

(b)  School  Nurses  and  Physical  Examinations.  • —  As 
children  are  compelled  by  law  to  attend  school,  it  is  the  duty 
of  the  school  officials  to  see  that  their  health  is  safeguarded 
in  every  way.  For  this  purpose  school  doctors  and  nurses  are 
employed  who  inspect  the  children's  health.  Their  throats, 
teeth,  eyes  and  ears  are  examined  by  experts  who  either  give 
or  suggest  skilled  treatment  for  physical  defects,  thereby 

removing  conditions  which  might  later  on  seriously  interfere 

with  health  and  usefulness. 

Specific  results  of  tonsil  and  adenoid  infections,  decayed 

teeth,  eye  strain,  and  ear  diseases  have  already  been  pointed 

out  in  the  sections  dealing  with  the  physiology  of  the  throat, 

mouth,  and  special  senses. 

Quarantine  Laws.  ■ —  By  the  term  quarantine  is  meant  the 

isolation  of  a  person  or  persons  having,  or  suspected  of  having, 

a  communicable  disease.     This  procedure  prevents  the  spread 


THE  CONTROL  OF  HEALTH  391 

of    communicable    diseases.     The    quarantine    period    may 
involve: 

1.  The  time  elapsing  between  exposure  and  onset  of  disease. 

2.  Time  of  actual  sickness  with  the  disease. 

3.  A  detention  period  after  active  sickness  is  past  but  during 

which  the  person  may  be  a  "carrier,"  i.  e.,  be  a  source 
of  infection  to  others. 

r  We  have  already  called  attention  to  the  "incubation" 
period  of  several  common  diseases  in  Chapter  XXIII.  The 
second  period  mentioned  will  differ  much  with  the  physio- 
logical condition  and  care  given  the  patient,  so  that  Httle  may 
be  said  about  it  in  advance.  The  period  of  detention  also 
varies  but  in  no  case  should  a  person  recovering  from  a  com- 
municable disease  be  allowed  to  return  to  the  company  of 
others  without  permission  from  a  physician.  The  quarantine 
law  for  some  minor  maladies  often  reads  thus:  "Persons 
suffering  from  measles,  whooping-cough,  mumps,  German 
measles,  and  chicken-pox  shall  be  barred  from  school  for 
twenty-one  days  from  the  onset  of  the  disease."  Lessening 
or  lengthening  of  this  period  is  left  to  the  physician  or  health 
officer  having  jurisdiction. 

Houses  in  which  there  are  communicable  diseases  should 
bear  a  placard  so  stating;  and  the  Board  of  Health  should 
furnish  a  list  of  communicable  diseases,  with  the  quarantine 
rules  applying  to  them,  to  all  parents  who  have  children  in 
school. 

Municipal  Health  and  Hygiene.  • —  From  the  standpoint 
of  health,  the  city  has  many  of  the  characteristics  of  the 
single  home.  As  the  ill  health  of  one  or  two  members  of  a 
family  may  endanger  the  health  of  the  rest,  in  precisely  similar 
fashion  unhealthful  conditions  in  any  section  of  a  city  are  a 
menace  to  the  whole  city.  Therefore  authority  must  be 
given  special  groups  of  men  who  shall  act  toward  affairs  of  a ' 
city  as  parents  do  in  the  affairs  of  families. 


392  ADVANCED   PHYSIOLOGY 

Public  Commissions  and  Boards  for  Safeguarding 
Public  Health.- —  The  Board  of  Health,  with  the  co-operation 
of  other  Commissioners  and  Committees,  keeps  vigil  over  the 
health  of  the  entire  city.  Other  bodies  which  act  with  them 
or  under  their  direction  are  the  Water  Commissioners,  Street 
Commissioners,  Milk  and  Food  Inspectors,  and  School  Nurses. 
Among  the  larger  responsibilities  of  such  pubHc  officials  are 
the  prevention  of  carelessness  as  to  food  and  water  supplies, 
condition  of  streets,  garbage  disposal,  the  prevalence  of  noise 
and  smoke,  the  ventilation  of  stores,  factories,  and  public 
buildings,  the  quarantine  of  infectious  diseases,  and  provision 
of  opportunities  for  securing  recreation  and  fresh  air  for  all 
classes.  Their  work  is  said  to  be  that  of  securing  public 
hygiene  in  contrast  to  that  science  and  observance  which 
makes  for  the  health  of  the  individual  and  is  called  personal 
hygiene. 

It  is  very  apparent  that  only  scientifically  trained  men 
should  be  chosen  members  of  Boards  of  Health,  for  the  lives 
of  hundreds,  or  hundreds  of  thousands,  are  in  their  hands. 

Public  Water  Supplies.  ■ — •  The  greatest  care  should  be 
exercised  to  secure  pure  water  for  towns  and  cities.  Public 
reservoirs  must  be  filled  from  sources  entirely  uncontaminated 
by  refuse  from  human  habitations  and  must  be  kept  pure. 
Leaves  and  dying  plants  should  not  be  allowed  to  collect  in 
them,  as  they  become  breeding  places  for  bacteria  and  other 
unicellular  organisms  injurious  to  health. 

Conduit  pipes  and  faucets  must  be  of  materials  which  will 
not  vitiate  the  water.  If  a  water  supply  is  taken  from  lakes 
or  rivers  which  are  unavoidably  contaminated,  it  should  be 
sterilized  chemically  or  otherwise,  and  thoroughly  filtered. 
No  dependence  should  be  placed  on  the  ordinary  small  faucet 
* 'filters'*  sold  for  private  use. 

Public  Food  Supplies:  Markets.  —  The  fitness  of  foods 
cannot  be  determined  unless  they  are  traced  to  their  sources, 
and  the  method  of  gathering,  packing,  shipping,  selling,  and 


THE  CONTROL  OF  HEALTH  393 

delivering  is  known.  Uncleanness  at  any  point  in  this  process 
unfits  the  article  for  use.  Contact  with  human  hands  always 
brings  in  a  source  of  danger;  exposure  in  stores  or  on  sidewalks 
gives  opportunity  for  infection  from  many  sources.  Many 
foods  deteriorate  if  left  at  temperatures  which  permit  bacteria 
to  increase  rapidly;  some  containers  have  surfaces  which,  under 
action  of  the  air  and  acids,  will  poison  the  contents.  All  fruits 
and  vegetables  which  are  not  cooked  before  eating  should  be 
thoroughly  washed. 

The  United  States  Government  and  the  various  State 
Governments,  as  well  as  municipalities,  have  passed  laws  and 
regulations  governing  the  production  and  sale  of  food  stuffs, 
such  as  the  seeding  of  raisins,  the  packing  of  figs  and  meat,  the 
wrapping  of  bread,  the  canning  of  vegetables  and  fruits,  and 
the  milling  of  flour.  Inspectors  are  appointed  to  see  that 
foods  offered  for  sale  comply  with  these  regulations. 

Highly  nutritious  foods  like  milk  are  especial  breeding  places 
for  bacteria  and  must  be  handled  with  extreme  cleanliness 
from  source  to  consumer.  Cows  must  be  healthy  (no  tuber- 
culous condition),  stables  sanitary,  milking  men  and  machines 
clean  (and  men  healthy),  cans  and  bottles  sterile.  With  the 
best  of  care  milk  receives  bacteria  from  the  air;  but  Grade  A 
milk  (for  infants)  should  not  contain  over  60,000  bacteria 
per  cCo  (if  Pasteurized,  not  over  30,000  per  cc).  Grade  B 
not  over  100,000  per  cc,  and  Grade  C  (used  only  for  cooking) 
not  over  300,000  per  cc. 

To  be  on  the  safe  side,  one  should  always  remember  that 
thorough  cooking  (boiling  temperatures  or  higher)  destroys  all 
living  matter.  Thus,  danger  from  infected  food  may  be 
avoided;  but  food  free  from  infection  is  safer  and  better  yet. 

Purity  also  impUes  freedom  from  adulterants;  coffee,  tea, 
spices,  syrups,  milk,  powdered  and  dry  * 'foods  "are  not 
infrequently  increased  in  bulk  and  weight  with  cheap  sub- 
stitute articles. 

Pork  should  be  free  from  trichina  worms,  oysters  from 


394  ADVANCED   PHYSIOLOGY 

typhoid  bactena,  cereals  and  meals  from  insect  eggs  and  the 
maggots  which  hatch  from  them,  vinegar  from  'Vinegar  eels." 

Public  Disposal  of  Garbage.  • —  At  each  of  the  many 
homes  in  a  city  there  accumulates  daily  an  unavoidable  quan- 
tity of  debris;  garbage  from  the  kitchen,  waste  paper,  empty 
food  containers,  ashes,  etc.  Such  material  cannot  be  disposed 
of  on  the  premises,  save  by  use  of  costly  incinerators  or  by 
burial.  A  system  of  collection  at  pubhc  expense  is  the  only 
safe  and  sure  way  of  securing  sanitary  disposal  of  such  material. 
"Filth  breeds  disease"  as  one  often  reads,  and  one  protects 
not  only  himself  but  all  about  him  when  he  insists  on  sanita- 
tion in  the  matter  just  mentioned.  Garbage,  if  not  burned 
immediately,  must  always  be  kept,  until  collected,  in  covered 
containers  which  will  keep  out  insects  and  vermin. 

Street  Cleaning.  • —  The  sources  of  dirt  and  filth  in  a  city 
are  innumerable.  To  some  extent  this  dirt  adheres  to  every 
one.  Air  currents  stir  it  up  and  carry  it  everywhere.  The 
accumulation  of  dirt  and  filth  in  a  city  should  either  be  washed 
away,  or  carried  to  stations  especially  fitted  for  burning  it  or 
to  places  where  it  may  be  buried.  The  city's  example  of 
cleanliness  or  lack  of  it  is  one  which  influences  the  practices  of 
all  the  inhabitants.  To  compel  this  public  cleanliness  by 
law  should  be  the  willing  procedure  of  the  people.  DisraeU, 
the  famous  Englishman,  once  said:  * 'Public  health  is  the  foun- 
dation on  which  reposes  the  happiness  of  the  people  and  the 
power  of  the  country.  The  care  of  the  public  health  is  the 
first  duty  of  a  statesman." 

Public  Playgrounds  and  Parks.  —  The  providing  of  play- 
grounds and  parks  is  necessary,  as  we  now  appreciate  the  vital 
relation  between  recreation,  fresh  air,  and  rest  on  the  one 
hand,  and  effectiveness,  health,  and  readiness  for  action  on 
the  other.  These  pubhc  playgrounds  and  parks,  with  the 
opportunities  they  afford  to  leave  the  crowded  sections  of  the 
city  with  their  barren  walls,  their  din,  smoke,  fatigue,  and 
monotony,  are  the  oases  in  the  city  desert.     Parks  ^xe  urmec- 


THE  CONTROL  OF  HEALTH  395 

essary  for  those  who  can  afford  their  own  ample  yards,  or  can 
quickly  reach  the  country  in  automobiles;  but  for  the  vast 
majority  who  have  no  other  source  of  out-door  relief,  they  are 
indispensable.  For  many  children  they  undoubtedly  mean 
the  difference  between  living  and  not  living. 

Medical  Inspectors  and  the  Control  of  Epidemics.  ^ — 
The  real  nature  of  communicable  diseases,  their  symptoms,  the 
sources  of  infection,  the  method  of  treatment,  the  liability  and 
manner  of  spreading,  and  the  seriousness  of  the  disease  to  the 
patient  is  known  only  by  those  well  trained  in  the  science  of 
medicine.  Medical  inspectors  are  given  legal  permission  and 
the  assigned  duty  of  keeping  track  of  the  pubHc  health.  They 
give  the  sick  prompt  attention  and  protect  others  from  infec- 
tion. Without  them  communicable  diseases  would  be  uncon- 
trolled and  without  proper  attention  one  case  might  easily 
spread  to  thousands.  It  is  the  duty  of  every  physician  to 
report  cases  of  communicable  disease  to  the  public  health 
officers  and  to  co-operate  with  them  in  every  possible  manner. 
The  people,  in  turn,  should  give  their  willing  support  to  the 
decisions  of  these  men. 


COMMON  EPIDEMICS  AND  THEIR  PREVENTION. 

Influenza.  —  The  nature  of  this  disease  has  been  already 
discussed.  A  person  sick  with  influenza  expels  the  infecting 
organisms  in  minute  droplets  of  mucus  when  sneezing,  cough- 
ing, laughing,  or  shouting.  The  fingers  of  a  patient  are 
probably  constantly  infected.  These  minute  droplets  con- 
taining the  infecting  organisms  are  inhaled  by  others  and 
infection  may  take  place. 

An  ordinary  infection  will  produce  illness  in  from  one  to 
four  days.  The  patient  should  be  isolated  and  the  case 
reported  to  the  Board  of  Health. 


396  ADVANCED  PHYSIOLOGY 

The  best  known  measures  to  avoid  the  spread  of  influenza 
are  the  following: 

1.  Prevent  the  crowding  of  people  together  in  homes, 
schools,  churches,  theatres,  cars,  etc. 

2.  Provide  plenty  of  ventilation. 

3.  Avoid  extremes  of  temperature. 

4.  Provide  ample  nourishment  and  take  recreative  exercise 
out  of  doors. 

Measles. — The  ca-use  of  this  disease  is  unknown.  The 
incubation  period  is  from  five  to  ten  days  (average  seven). 
A  patient  may  **give"  the  disease  to  others,  however,  five  days 
before  he  is  aware  that  he  has  the  disease.  The  most  infective 
stage  is  when  the  patient  is  first  * 'breaking  out." 

To  prevent  epidemics  the  following  precautions  should  be 
observed : 

1.  All  cases  should  be  reported  and  isolated  for  five  days 
after  ** breaking  out." 

2.  Those  exposed  should  refrain  from  contact  with  others 
for  fifteen  or  eighteen  days.  Exceptions  to  this  are  those  who 
have  had  measles  earlier,  as  they  are  permanently  immune. 

3.  Avoid  contact  with  people  by  keeping  away  from  crowds, 
particularly  indoor  gatherings. 

Disinfection  of  rooms  recently  occupied  by  measles  patients 
seems  to  be  unnecessary.  Middle-ear  infection  is  the  most 
common  consequence  of  measles,  while  diphtheria  and  pneu- 
monia following  measles  are  often  fatal. 

Cerebro-spinal  meningitis.  —  Epidemics  of  this  disease 
occur  in  late  winter  and  spring,  and  among  children  below  five 
years,  or  young  people  between  sixteen  and  twenty-four 
years  of  age.  This  disease  is  spread  by  discharges  from  the 
mouth  and  nose ;  and  many  carry  the  disease  germs  and  infect 
others,  without  themselves  being  sick.  Such  people  are 
called  ''carriers." 


THE   CONTROL  OF   HEALTH  397 

The  incubation  period  is  unknown.  Protective  measures 
are: 

1.  Isolation. 

2.  Extreme  care  to  disinfect  and  destroy  all  materials 
expelled  from  the  mouth  and  nose;  these  should  be  collected 
in  gauze  cloths  and  burned. 

Typhoid  Fever.  ^ — This  disease  is  known  to  spread  in  no 
wa}^  except  through  the  swallowing  of  bacteria  from  the 
excreta  of  a  previous  case.  Sickness  sets  in  from  eight  to 
fourteen  days  after  infection. 

Epidemics  are  prevented,  or  if  under  way,  may  be  controlled 
in  these  ways : 

L  Rigid  examination  of  all  foods  and  drinks,  to  insure 
purity  and  sterility. 

2.  Prohibition  of  sale  of  food  and  drink  by  peddlers. 

3.  Prevention  of  transmission  by  flies,  by  screening  houses 
and  destroying  breeding  places  of  flies. 

4.  ''Carriers"  should  be  identified,  isolated,  and  "cured." 

5.  Careful  sterilization  of  all  dishes  used  by  patient. 

6.  Insistence  upon  general  use  of  typhoid  serum. 

Mumps. ^ — The  cause  of  this  disease  is  unknown.  Its 
manner  of  spreading  is  by  the  saliva  which  is  often  on  fingers 
which  have  been  purposely  or  thoughtlessly  put  into  the 
mouth.  Anything  they  touch  is  then  infected,  and  passes 
on  germs  to  any  other  person  who  may  touch  it. 

The  incubation  period  is  from  one  to  three  weeks. 

Epidemics  of  mumps  are  partially  avoided  at  least  by: 

1.  Isolating  patients. 
L    2.  Guarding  against  infection  of  anything  with  saliva. 
F    3.  Avoiding  infection  droplets  from  a  patient. 

Scarlet  Fever.  • — This  disease  is  not  as  epidemic  as  many 
others  and  concerns  chiefly  young  people.  The  cause  is 
unknown;  the  incubation  period  is  from  one  to  seven  days. 


398  ADVANCED  PHYSIOLOGY 

Transmission  is  through  droplets  or  smears  from  the  mem- 
branes of  the  mouth  and  air  passages.  * 'Carriers"  are  respons- 
ible for  many  cases.  However,  many  epidemics  are  believed 
to  have  been  caused  by  milk  which  had  become  infected  during 
handling. 

Its  spread  may  be  hindered  or  stopped  by: 

1.  Avoiding  crowding  of  people  together. 

2.  Pasteurizing  all  milk  supphes. 

3.  Isolation  of  patients. 

4.  Disinfection  of  all  discharges  from  the  mouth  or  nose.     - 

Scales  from  the  skin  probably  have  no  special  infective 
power,  and  rooms  once  occupied  by  patients  may  be  dis- 
infected with  formaldehyde  if  desired;  this  precaution  is 
probably  unnecessary. 

If,  after  learning  and  perhaps  experiencing  some  of  the 
modern  methods  of  health  conservation,  some  are  tempted  to 
feel  that  such  procedures  interfere  with  personal  liberties, 
they  should  remember  that,  in  the  long  run,  personal,  family, 
neighborhood,  school,  and  municipal  health  and  hygiene  are 
so  closely  interdependent  that  authority  must  be  present  at 
every  point ;  also  that  observance  of  legislation  looking  toward 
the  greatest  common  good  should  be  accorded,  not  grudgingly, 
but  eagerly  and  sympathetically  by  all. 


DEMONSTRATIONS  OR  LABORATORY  EXERCISES 

The  following  directions  are  made  on  the  supposition  that  no  teacher 
will  be  giving  instruction  in  Physiology  who  has  not  had  specific  prepara- 
tion for  it,  and  will  therefore  be  able  to  comprehend  the  significance  of 
each  suggestion,  and  know,  in  a  general  way  at  least,  how  to  proceed  with  it. 

A  hst  of  firms,  from  whom  many  materials  called  for  can  be  obtained,  is 
here  given,  as  also  formula?  for  the  making  of  necessary  gases  and  reagents, 
and  a  table  of  equivalents  between  the  English- American  units  of  measure 
and  those  of  the  metric  system.  By  anticipating  the  class  or  laboratory 
in  a  reasonable  manner  no  difficulty  will  be  found  in  making  nearly  every 
page  of  the  text  vivid  and  scientific  in  its  presentation. 

The  chapter  and  page  numbers  refer  to  the  relevant  chapter  and  page 
in  the  body  of  the  text. 

CHAPTER  I 

Page  12.  —  Numerous  forms  of  protozoa  can  be  easily  obtained  from 
dishes  containing  decaying  pond  plants,  barely  covered  with  water,  which 
have  been  standing  quietly  a  couple  of  weeks,  and  may  be  studied  by 
placing  them  in  a  drop  of  water  under  a  microscope. 

Page  15.  —  Cells  are  easily  shown  by  use  of  prepared  slides.  (See  sources 
of  material  and  apparatus,  page  421.) 

Fresh  cells  can  be  shown  under  a  microscope  as  follows :  in  very  thin 
cross  sections  of  plant  stem,  e.g.  corn  stalk,  lily ;  blood  cells  from  frog, 
or  in  blood  from  finger  prick ;  in  thin  bit  of  cartilage  from  upper  end  of 
femur  bone  of  frog ;  in  the  thin  tail  of  tadpole  of  frog,  toad,  or  salamander. 

Page  17.  —  Living  protoplasm  can  be  «een  easily  in  live  Amoebae,  gen- 
erally found  in  dishes  of  decaying  pond  plants;  in  cells  of  pond  weed 
Nitella,  or  Chara ;  or  in  hair  cells  from  leaf  of  Tradescantia  ("  Wandering 
Jew  ") ;  high  powers  of  microscope  required. 

Page  23.  —  Set  aside  (1)  pond  scum  and  weeds  in  dish  with  just  enough 
water  to  cover,  for  2  weeks ;  (2)  hay  in  water  (preferably  in  water  in 
which  other  hay  has  been  boiled,  and  then  cooled). 

Many  unicellular  animals  will  be  found  in  a  drop  of  this  material  under 
microscope.     See  also  addresses  of  firms  who  sell  this  material. 

399 


400  ADVANCED  PHYSIOLOGY 


CHAPTER  n 

Page  27.  —  Show  the  class  some  charcoal,  graphite  ("  lead  "  of  a  lead 
pencil),  and  some  lampblack,  caUing  attention  to  the  fact  that  they  are 
the  same  chemical  element,  carbon.  Light  a  bit  of  candle  and  cover  with 
a  bell  glass.  The  candle  soon  goes  out.  Explain  that  the  carbon  has 
combined  with  the  oxygen  in  the  air  to  form  a  new  compound,  CO2  or 
carbon  dioxid. 

Show  the  class  specimens  of  phosphorus,  sodium,  potassium,  iron  and 
sulfur.  Place  a  little  sulfur  in  an  earthen  dish  and  ignite  it.  It  burns 
with  a  blue  flame  and  gives  off  a  suffocating  gas.  It  has  combined  with 
the  oxygen  of  the  air,  forming  by  oxidation  a  new  compound,  SO2  or  sulf  ar 
dioxid. 

Page  29.  —  Tests  should  be  made  on  a  variety  of  common  foods  to 
prove  the  presence  of  proteid.  White  of  egg,  meat  juice,  ground  oat- 
meal, show  the  test  readily.  With  a  solution  of  any  one  of  them  in  water 
in  a  test  tube  (use  10  cc.  or  so)  add  a  little  strong  nitric  acid  and  heat  to 
boiling;  note  the  yellow  color.  Add  ammonia,  and  note  the  orange 
color  (Xanthoproteic  reaction). 

With  rather  weak  solution  of  same  material  in  test  tube,  add  a  little 
1  %  sol.  copper  sulfate,  then  a  little  caustic  potash ;  a  violet  color  shows 
presence  of  proteid. 

Try  same  reagents  with  starch  and  sugar  solutions,  and  show  that  the 
tests  are  negative. 

The  gluten  content  of  flour  can  be  shown  by  putting  a  quantity  of 
flour  in  a  mushn  bag  and  thoroughly  kneading  it  in  a  pail  of  water.  Much 
of  the  bulk  will  wash  out  into  the  water ;  the  gluten  will  be  left  as  a  sticky, 
undissolved  mass  in  the  bag. 

Pour  a  Uttle  hydrochloric  acid  into  a  small  amount  of  milk.  The 
curd  which  forms  is  largely  casein. 

Fibrin  can  be  obtained  from  perfectly  fresh  blood  by  stirring  it.  The 
fibers  which  catch  on  the  object  used  in  stirring  are  fibrin. 

Myosin  can  be  shown  in  finely  minced  lean  meat  by  soaking  it  in  a 
little  water  for  a  few  hours,  and  then  pouring  strong  acid  (nitric)  into  some 
of  the  juice.     The  material  which  coagulates  is  myosin. 

Page  31.  —  (a)  Shake  up  a  little  corn  or  potato  starch  with  water  in 
test  tube  and  add  a  few  drops  of  an  iodine  solution.  A  typical  blue- 
color  reaction  will  appear.  Ground  rice,  flour,  and  cereal  also  respond 
readily.  Use  the  same  test  on  white  of  egg  or  sugar  solution  to  prove 
validity  of  test. 


LABORATORY  EXERCISES  401 

(h)  Put  a  few  drops  of  1%  copper  sulfate  solution  in  test  tube,  and 
add  solution  of  grape  sugar  (dextrose) ;  then  add  a  few  drops  of  strong 
caustic  potash  solution  and  boil ;  a  rust-red  precipitate  is  formed  in  bot- 
tom of  tube  (cuprous  hydrate  or  oxide). 

If  cane  sugar  is  used,  the  above  result  will  not  follow  unless  the  sugar 
solution  is  first  treated  with  a  few  drops  of  25%  solution  of  sulfuric  acid 
and  then  boiled ;  after  this  treatment,  proceed  as  in  case  of  dextrose  and 
same  result  follows.     Unmodified  cane  sugar  does  not  contain  dextrose. 

Test  starch  or  white  of  egg  in  the  same  way  and  show  that  the  reaction  is 
negative. 

Page  32.  —  Put  a  small  bit  of  fat  meat  (of  size  of  pea  is  sufficient)  in 
test  tube  and  then  pour  in  a  little  1%  solution  of  osmic  acid.  The  fat 
turns  black. 

Place  a  few  drops  of  olive  oil  in  a  test  tube  with  a  little  water  and  shake 
vigorously.  The  oil  forms  a  milky  white  emulsion.  Examine  a  drop  of 
milk  with  a  microscope,  and  note  the  fat  globules  forming  an  emulsion. 
Put  a  small  bit  of  fat  meat  on  a  perfectly  clean  slide,  pour  on  a  little  ether 
and  allow  to  evaporate;  the  ether  dissolves  the  fat  ahd  on  evaporation 
leaves  a  scum  on  the  glass. 

Tests  of  same  sort  with  proteids  or  carbohydrates  give  negative 
results. 

Page  34.  —  Boil  tough,  gristly  pieces  of  meat  and  cut  bones  in  a  little 
water.  A  jelly  will  form  as  the  solution  cools,  which  illustrates  the 
nature  of  gelatin. 

CHAPTER  III 

Page  37.  —  Since  the  character  of  the  teeth  is  an  indication  of  what  an 
animal  eats,  it  will  be  instructive  to  show  different  sorts  of  skulls  with 
teeth  in  position ;  e.g.  the  human  teeth  indicate  omnivorous  diet ;  the  rab- 
bit teeth  indicate  herbivorous  diet ;  the  cat  or  dog  teeth  indicate  carnivo- 
rous diet. 

Page  40.  —  Boil  an  egg  for  ten  minutes  and  remove  the  shell.  Cut  in 
halves  to  show  the  coagulated  albumen  and  the  yolk.  Put  some  of  the 
coagulated  white  in  water  and  heat  to  prove  that  it  will  not  dissolve. 
The  white  of  raw  egg  coagulates  in  strong  acid  the  same  as  in  boiling 
water. 

Page  42.  —  The  proteid  value  of  foods  will  be  made  more  vivid  if  a 
considerable  list  of  foods  is  on  hand  in  quantities  which  can  be  used  in 
connection  with  the  table. 


402  ADVANCED  PHYSIOLOGY 

Page  43.  —  Cut  a  raw  potato  and  place  some  iodine  upon  the  cut 
surface.  Treat  a  bean  that  has  been  soaked  in  water  for  a  day  in  the  same 
way.     Which  shows  the  more  starch? 

By  definite  trials,  prove  that  egg  albumen,  meat,  flour,  and  sugar  do  not 
react  in  uniform  ways  to  this  treatment.     The  test  is  specific  for  starch. 

Page  45.  —  With  a  thermometer  it  will  be  easy  to  ascertain  the  melting 
point  of  some  fats,  e.g.  butter,  lard,  pork  fat,  and  mutton  fat ;  then  com- 
pare with  temperature  of  the  body. 

Page  54.  —  With  very  sharp  razor  prepare  very  thin  sections  of  raw  and 
cooked  potato;  place  under  a  microscope  and  demonstrate  the  points 
here  mentioned. 

Page  55.  —  Prepared  slides  of  pork  muscle  infected  with  trichina  are 
obtainable  from  nearly  any  dealer  in  microscopical  preparations.  Con- 
sult address  list  in  another  part  of  Appendix  for  partial  Ust  of  dealers. 

CHAPTER   IV 

Page  63.  —  Fill  a  test  tube  half  full  of  a  solution  of  molasses  (better 
than  this  is  Pasteur's  solution)  and  to  it  add  a  little  yeast  from  an  ordinary 
yeast  cake.  Let  the  mixture  stand  in  a  warm  place  for  several  hours. 
CO2  gas,  due  to  fermentation,  will  appear  as  bubbles.  To  prove  the  nature 
of  this  gas,  take  a  larger  amount  of  the  fermenting  mixture  in  a  flask,  and 
conduct  the  gas  by  a  tube,  as  shown  in  Figure  26,  into  limewater;  a 
white  precipitate  in  the  latter  proves  the  presence  of  CO2.  After  a  time, 
the  formation  of  alcohol  in  the  sugar  mixture  can  be  detected  by  its  odor. 

To  make  this  demonstration  more  vivid  and  complete,  the  fermenting 
solution  should  be  put  into  flask,  over  opening  of  which  a  rubber  tube  is 
fitted,  this  in  turn  being  connected  to  glass  tube  which  can  be  led  through 
a  stream  of  water ;  then  boil  the  liquid,  and  the  vapor  will  be  condensed 
in  the  cold  glass  tube  and  thus  alcohol  can  be  collected  in  liquid  form. 
This  carries  out  the  principle  of  a  still. 

Page  64.  —  Mix  starch  and  water  in  a  small  beaker.  Heat,  stirring 
constantly,  and  note  how  the  mixture  thickens  owing  to  the  bursting  of 
the  starch  grains  and  the  absorption  of  water. 

Place  a  little  of  the  mixture  in  a  test  tube  and  by  the  method  used  in 
the  demonstration  for  page  31  determine  that  it  contains  no  sugar.  In 
another  test  tube  mix  a  small  portion  of  the  starch  solution  with  plenty 
of  saliva.  Be  very  sure  that  the  test  tube  is  perfectly  clean ;  a  trace  of 
acid  in  it  will  prevent  the  desired  result  in  this  experiment.  Place  the 
saliva  and  starch  mixture  in  a  beaker  of  water.     Heat  the  latter  to  about 


I 


LABORATORY  EXERCISES  [403 

le  temperature  of  the  body  and  let  it  stand  for  about  ten  minutes. 
Then  test  for  sugar.  A  typical  reaction  should  appear.  The  sweet  taste 
of  bread  (a  starchy  food),  after  being  in  the  mouth  for  a  while  is  well 
known. 

Examine  saliva  under  a  microscope  to  note  the  absence  of  any  fermenting 
bodies,  like  yeast. 

Page  67.  —  1.  To  see  yeast  cells,  examine  a  mixture  of  yeast  and  water 
with  a  microscope  (high  power). 

2.  Set  aside,  in  a  warm  place,  any  food  material  such  as  piece  of  meat, 
in  small  receptacle ;  barely  cover  with  water,  and  leave  for  two  or  three 
days.  Then  examine  a  drop,  covered,  under  microscope  with  high  powers, 
for  numerous  forms  of  bacteria.  They  have  almost  no  color,  and  much 
care  must  be  used  in  having  just  the  right  degree  of  illumination. 

With  a  dull  edged  instrument  (e.g.  spoon  handle)  scrape  a  little  material 
from  inside  lining  of  the  cheek,  or  take  a  little  material  from  between  the 
teeth  with  tooth-pick;  place  this  in  a  little  water  under  cover-sUp  and 
examine  as  above.  Bacteria  will  be  numerous,  perhaps  loose  epithelial 
cells  also. 

Page  73.  —  Fill  four  test  tubes  one-third  full  of  water.  Place  in  two 
of  them  a  small  bit  of  meat  and  in  the  other  two  a  little  white  of  egg. 
Plug  all  four  with  cotton.  Place  one  of  each  set  of  two  in  a  beaker  of 
water  and  boil  briskly  for  ten  minutes.  Set  all  four  aside.  Examine  after 
two  days  and  again  after  four  days. 

Many  bacteria  will  appear  in  the  unboiled  tubes,  with  characteristic 
decomposition  odors ;  the  boiled  tubes  will  show  no  deterioration. 

CHAPTER  V 

Page  76.  —  1.  A  human  skull  should  be  at  hand  for  direct  reference 
to  the  teeth.  Separate  teeth  to  show  roots,  etc.,  can  usually  be  obtained 
from  a  dentist.  Other  skulls  containing  teeth  are  useful  to  show  differ- 
ent shapes  in  animals  of  different  habits.  Teeth  of  a  rabbit  or  horse  are 
very  different  from  those  of  a  carnivorous  animal,  e.g.  cat  or  dog. 

2.  The  layers  of  a  tooth  can  be  easily  shown  by  use  of  prepared  sections. 
See  list  of  dealers  in  shdes. 

A  model  of  a  tooth  can  be  rather  easily  cut  from  piece  of  hard  soap. 

Page  77.  —  Dip  a  bit  of  blue  litmus  paper  into  a  little  dilute  hydro- 
chloric acid,  and  note  that  it  turns  red.  In  the  same  way  test  vinegar, 
lemon  juice,  and  sour  milk.  Dip  a  bit  of  red  Utmus  paper  into  an  alkaline 
liquid,  like  ammonia.  Test  soapsuds  in  the  same  way.  Determine  whether 
saliva  is  acid  or  alkaline. 


404  ADVANCED  PHYSIOLOGY 

Page  78,  —  To  illustrate  the  action  of  an  acid  on  the  teeth,  show  the 
result  of  putting  hydrochloric  acid  on  an  egg  shell.  Rapid  corrosion 
follows. 

Page  79.  —  The  correctness  of  the  text  figure  can  be  easily  proved  by  use 
of  prepared  slides  of  taste  buds.     See  list  of  dealers. 

Page  80.  —  The  connection  between  the  nose  and  mouth  cavities 
through  the  pharynx  is  easily  shown  by  merely  noting  that  any  breath 
drawn  in  through  the  mouth  can  be  expelled  through  the  nose,  or  vice 
versa. 

This  point  may  also  bs  illustrated  by  use  of  human  skull,  or  if  this  is 
not  at  hand,  by  the  skull  of  cat,  dog,  rabbit,  etc. 

Page  81.  —  The  salivary  glands  of  a  cat  show  readily  as  soon  as  the 
skin  is  removed  from  the  head,  and  in  same  location  as  in  man.  The 
duct  from  the  parotid  gland  passes  across  the  cheek  region  and  no  dissec- 
tion is  required  to  show  most  of  its  length. 

Page  84.  —  Ciliary  action  can  be  easily  shown  under  high  powers  of 
a  compound  microscope  by  mounting  on  a  glass  slide  (in  0.6%  salt  solu- 
tion) some  ciliated  cells  scraped  from  roof  of  a  frog's  mouth,  or  a  piece  of  a 
clam's  gill.     A  correct  idea  of  cilia  cannot  be  obtained  otherwise. 

The  surprising  power  of  cili..  to  move  objects  is  demonstrated  by  remov- 
ing the  lower  jaw  and  floor  of  mouth  complete  from  frog  after  brain  has 
been  destroyed.  Keeping  the  surface  of  roof  of  mouth  moist  with  normal 
saline  solution  (0.6%)  place  on  it  a  small  wooden  block,  size  of  pea.  It 
will  be  moved  along  by  the  cilia. 

Page  84.  —  1.  If  one  closes  the  nose  passages  by  holding  the  nose  between 
the  fingers,  and  then  swallows,  the  noise  in  the  ears  shows  that  a  passage 
exists  between  them  and  the  throat. 

A  model  of  the  human  pharynx  should  be  used  in  this  connection. 

2.  The  several  openings  into  the  pharynx  described  in  Chapter  V 
can  easily  be  shown  in  a  recently  chloroformed  frog.  The  glottis  is  a 
longitudinal  slit  on  a  slight  prominence  at  the  back  of  the  tongue.  The 
gullet  is  immediately  back  of  the  glottis.  The  posterior  openings  of  the 
nostrils  are  just  back  of  the  upper  jaw,  at  the  very  front  of  the  mouth. 
The  Eustachian  tubes  can  be  seen  as  wide  openings  at  the  junction  of 
upper  and  lower  jaws ;  a  bristle  can  easily  be  passed  into  them  co  as  to 
demonstrate  that  the  passage  leads  to  the  ear. 


LABORATORY  EXERCISES  405 

CHAPTER  VI 

Page  90. —  The  body  cavity,  its  divisions  and  contained  organs,  should 
be  made  plain  by  use  of  a  manikin. 

If  some  animal  such  as  cat,  rabbit,  white  rat,  or  the  like  can  be  dissected, 
the  entire  teaching  of  the  body  cavity  and  contained  organs  can  be  very 
easily  made  clear. 

Page  94.  —  Coagulate  some  white  of  egg  in  boiling  water  in  a  beaker. 
Note  that  water  alone  will  not  dissolve  such  proteid.  Put  a  piece  of  egg 
as  large  as  the  end  of  one's  little  finger  (mincing  it  first)  into  a  test  tube 
half  full  of  artificial  gastric  juice  (see  formula).  Stand  the  test  tube  in  a 
beaker  of  water  kept  at  about  body  temperature  (98°)  and  note  that  the 
egg  slowly  dissolves.  When  it  has  gone  into  solution,  add  copper  sulfate 
and  caustic  potash ;  a  rose-red  color  instead  of  violet  shows  that  the  pro- 
[  teid  has  been  changed  into  peptone. 

Page  94.  —  A  solution  of  rennet  can  be  obtained  from  any  druggist, 
and  its  action  on  milk  shown  by  merely  adding  a  little  to  a  tube  of  warm 
milk  and  allowing  it  to  stand  for  about  |  hour. 

CHAPTER  VII 

Page  99.  —  A  very  useful  demonstration  of  the  intestine  with  arteries 
and  veins  injected,  and  the  whole  made  translucent,  can  be  obtained  from 
the  W.  H.  Welsh  Manufacturing  Company,  1516  Orleans  St.,  Chicago. 

Page  100.  —  The  teacher  should  demonstrate  all  the  organs  described 
in  this  chapter,  as  well  as  details  like  the  mesentery,  gall  bladder,  etc., 
by  use  of  a  manikin  of  the  human  body,  or  by  the  dissection  of  some  small 
mammal.  Even  a  fish  shows  much  of  interest  in  this  connection,  but 
has  no  diaphragm  and  is  unlike  the  human  in  numerous  ways. 

Page  101.  —  The  bile  duct,  gall  bladder,  and  liver  lobes  are  very  easily 
dissected  in  the  dog-fish. 

Page  103.  —  Artificial  pancreatic  juice  should  be  placed  in  a  test  tube 
with  coagulated  white  of  egg,  kept  at  body  temperature,  and  the  test  for 
peptones  made.  Starch  should  be  treated  in  the  same  way,  and  after  its 
digestion,  tests  made  for  sugar. 

To  show  action  of  pancreatic  secretion  on  fats  it  is  best  to  imitate  the 
conditions  present  in  the  intestine  by  mixing  with  the  artificial  pancreatic 
juice  a  little  white  of  egg,  as  other  things  besides  fat  are  always  present. 
Pour  into  such  a  mixture  some  olive  oil  and  shake  vigorously.  The  emul- 
sion thus  formed  will  not  separate  as  does  a  mixture  of  oil  and  water, 


406  ADVANCED  l>HYglOLOGY 

and  a  drop  of  it  should  be  examined  under  a  microscope  and  coinpared 
with  milk. 

CHAPTER  VIII 

Page  115.  —  Cover  the  bulb  end  of  a  thistle  tube  with  some  membrane 
like  the  lining  of  an  egg  shell  or  a  piece  of  goldbeater's  skin,  tying  it  tightly. 
Fill  the  bulb  with  solution  of  glucose,  holding  the  bulb  in  dish*  of  water 
while  doing  so  to  avoid  breaking  the  membrane,  which  is  very  thin.  Then 
lower  bulb  into  the  water  till  glucose  and  external  water  show  the  same 
level.  Fasten  the  tube  in  this  position ;  the  water  will  pass  into  the  glucose 
solution  through  the  membrane,  till  glucose  level  is  much  the  highest. 
This  occurs  against  the  force  of  gravity,  under  no  compulsion  except  that 
of  osmotic  pressure. 

Page  120.  —  The  lacteal  branches  of  the  lymphatic  system  which  arise 
in  the  walls  of  the  intestine  may  be  plainly  shown  in  the  mesentery  of  a 
cat  or  dog,  if  the  animal  is  chloroformed  about  three  hours  after  it  has 
eaten  freely  of  fatty  meat  and  milk.  On  opening  the  abdomen  imme- 
diately after  death,  the  mesentery  holding  the  intestine  will  be  seen  filled 
with  numerous  tiny  ducts  full  of  white,  fatty  emulsion. 

CHAPTER  IX 

Page  123.  —  The  plasma  and  corpuscles  in  blood  can  be  shown  by  put- 
ting a  drop  of  fresh  blood  from  a  prick  in  the  tip  of  the  finger  on  a  glass 
slide,  with  a  little  0.6%  solution  of  common  salt.  It  is  not  possible  to 
demonstrate  the  platelets  except  by  special  methods.  Frog's  blood  is 
also  easily  obtained.  For  permanent  mounts  of  the  blood  see  address 
list  of  dealers. 

Page  125.  —  1.  Defibrinated  blood  may  be  procured  from  a  butcher, 
by  catching  blood  directly  from  some  animal  and  stirring  it  immediately, 
thus  removing  the  fibrin  as  it  forms.  Blood  so  treated  will  not  clot  and 
will  keep  for  some  time.  Put  some  in  a  large  test  tube,  and  by  means  of 
a  glass  tube  opening  into  the  bottom  of  the  test  tube  run  oxygen  gas 
through  the  blood.  The  bubbles  which  will  be  thus  formed  will  be  of 
bright  red  color  (oxyha3moglobin) .  For  methods  of  making  this  gas, 
see  Appendix,  "  Formulae  and  Methods." 

2.  The  blood  of  a  guinea  pig,  rat,  or  dog  is  best  for  showing  oxyhaemoglo- 
bin  crystals.  It  is  not  so  readily  shown  in  human  blood.  The  amount 
of  ether  used  should  be  only  a  fraction  of  that  of  the  blood.  If  blood 
is  merely  mounted  in  water  and  allowed  to  stand  some  time,  crystals 
form  to  some  extent. 


LABORATORY  EXERCISES  407 

Page  127.  —  Prepared  slides  of  blood  are  very  useful  here ;  see  address 
list  of  dealers. 

Page  129.  —  Arrangements  may  be  made  with  a  butcher  to  fill  a  pint 
glass  container  with  fresh  blood;  this  should  be  set  aside  immediately 
and  left  undisturbed  until  the  blood  has  completely  clotted.  The  less 
the  specimen  is  disturbed  before  being  shown  in  a  classroom,  the  better. 
The  serum  will  appear  as  a  clear  fluid  about  the  clot;  the  latter  will 
shrink,  but  will  retain  the  shape  of  the  container.  Clean  fibrin  can  be 
obtained  by  kneading  a  clot  in  water ;  the  longer  it  is  washed  the  better. 
It  can  then  be  preserved  in  4%  formalin,  for  use  at  any  future  time. 

Page  131.  —  Dealers  will  furnish  prepared  slides  of  numerous  sorts  of 
bacteria,  including  the  types  here  mentioned.  They  also  furnish  sUdes 
of  blood  showing  the  malarial  organism,  Plasmodium  malariae. 

Page  133.  —  It  will  be  worth  while  to  procure  and  show  "  wrigglers  " 
and  pupae  of  mosquitoes,  as  well  as  adults,  or  parts  of  them,  under  low 
power  lenses.  The  young  are  easily  obtainable,  as  a  rule,  from  any  woods 
pond  in  early  spring.  Prepared  slides  of  mosquito  mouth  parts  are  pur- 
chasable. 

CHAPTER  X 

Page  137.  —  Obtain  a  turtle  if  possible,  as  it  will  show  more  satisfactorily 
than  any  other  animal  the  external  events  of  a  heart-beat.  Action  con- 
tinues a  long  time  after  the  head  is  removed. 

Page  138.  —  If  time  and  opportunity  permit,  the  teacher  may  show  the 
heart  of  a  beef  or  calf  to  the  class,  demonstrating  the  structure  and  action 
of  this  organ.  Instructions  should  be  given  the  butcher  to  leave  the  blood 
vessels  connected  with  the  heart  long,  i.  e.  the  pulmonary  artery  and  the 
aorta  should  be  severed  not  less  than  five  inches  from  their  exit  from  the 
heart.     The  pericardium  should  be  left  on. 

Before  class  period  the  specimen  should  be  trimmed  of  all  rough  ends  of 
tissues ;  the  blood  vessels  should  be  nicely  dissected  out  from  the  mass  of 
tissue  which  surrounds  them ;  in  doing  this  the  pericardium  will  be  cut 
away  in  part,  but  should  be  left  cs  perfect  as  possible.  The  external 
appearance  of  auricles  and  ventricles,  the  elasticity  of  the  blood  vessels, 
•  the  contrast  between  arteries  and  veins,  will  be  easily  noted.  If  the  follow- 
ing order  of  procedure  is  observed,  practically  every  feature  of  anatomy 
and  function  of  the  internal  parts  can  be  readily  shown. 

Cut  away  the  pericardium.  Shut  off  the  pulmonary  artery  with  a 
strong  clamp,  as  far  from  the  heart  as  possible.  Cut  through  the  wall  of 
the  right  ventricle  toward  the  apex  of  the  heart  j   carry  this  cut  forward 


408  ADVANCED  PHYSIOLOGY 

carefully  and  remove  most  of  the  right  ventricular  wall,  but  do  not  get 
within  an  inch  of  the  semilunar  valves  of  the  pulmonary  artery.  At  this 
point  the  tricuspid  valve,  chordae  tendinae,  and  papillary  muscles  of  this 
side  of  the  heart  are  fully  exposed.  If  the  conveniences  of  a  water  faucet 
and  sink  are  at  hand,  slip  over  the  faucet  opening  a  rubber  tube  (about  a 
yard  long)  in  the  end  of  which  is  a  piece  of  glass  tubing,  both  ends  of  which 
have  been  made  smooth  by  heating.  Insert  the  tube  between  the  semilunar 
valves  and  fill  the  artery  with  water  till  it  swells  under  the  pressure  ;  when 
very  full,  quickly  draw  out  the  tube ;  the  semilunar  valves  will  completely 
close  and  prevent  the  escape  of  water.  If  the  specimen  is  held  up  to  the 
light,  the  position  of  the  valves  and  their  perfect  closure  of  the  aperture 
can  be  clearly  shown. 

The  action  of  the  other  type  of  heart  valve  can  be  shown  as  follows : 
First  follow  the  aorta  downward  into  the  substance  of  the  base  of  the  heart, 
till  the  two  coronary  arteries  are  found;  these  must  be  tied  off  (with  a 
broad  cord,  as  the  tissues  are  soft  and  easily  cut  by  a  small  ligature)  or  the 
rest  of  the  experiment  will  not  succeed.  Now  cut  off  the  top  of  the  left 
auricle ;  the  peculiar  internal  structure  of  an  auricle  is  thus  seen.  Clamp 
off  the  aorta,  as  near  its  end  as  possible.  Thrust  the  water  tube  down 
through  the  auriculo- ventricular  opening,  and  fill  with  water.  The  left 
ventricle  will  first  fill,  and  from  there  the  water  will  go  into  the  aorta  and 
fill  that.  In  the  meantime,  the  two  flaps  of  the  mitral  valve  have  risen 
and  perfectly  closed  the  entrance  to  the  ventricle.  When  the  internal 
pressure  of  the  water  has  become  considerable,  draw  out  the  tube,  and  the 
heart  can  then  be  manipulated  to  show  better  the  valves  in  their  closed 
position.  After  this,  the  ventricle  can  be  cut  open,  the  thickness  of  its 
walls  compared  with  that  of  the  right  ventricle,  the  extreme  thinness 
of  the  wall  at  the  apex  of  the  heart  shown,  and  any  other  points  which 
the  instructor  wishes  to  bring  out. 

Do  not  fail  to  cut  out  the  semilunar  valves  and  place  in  formalin  for 
future  use. 

Pages  143.  —  To  one  end  of  a  piece  of  thin  rubber  tubing  about  three 
feet  long  attach  a  syringe  bulb  by  means  of  which  water  can  be  forced 
through  the  tube.  Into  the  other  end  of  the  tube  insert  a  glass  cannula, 
drawn  fine,  in  imitation  of  a  capiUary.  As  the  bulb  is  pressed  rhythmi- 
cally a  regular  pulse  can  be  felt  in  the  tube  by  holding  it  between  the  thumb  ■ 
and  finger.  It  can  be  shown  a  large  class  by  connecting  the  short  arm  of  a 
horizontal  lever  with  the  tube  by  means  of  an  upright  strip  of  wood,  or 
other  material ;  see  figure  on  opposite  page.  The  amount  of  "  pulse  "  or 
change  in  diameter  of  the  tube  will  be  increased  in  proportion  to  the 
differences  between  the  lengths  of  the  arms  of  the  lever. 


LABORATORY   EXERCISES 


409 


Page  145.  —  Count  the  pulse  rate ;  then  run  up  stairs  and  down,  or 
50  yards  and  back,  and  make  recount  of  the  rate.  Try  effect  of  holding 
the  breath. 

Page  147.  —  A  permanent  preparation  of  a  frog  with  arteries  injected 
is  purchasable,  and  very  suggestive  for  the  study  given  here.  If  laboratory 
work  is  given,  fill  arteries  with  starch  mass  (see  formula),  by  injecting 
forward  through  the  truncus  arteriosus  (big  vessel  leaving  the  heart), 
tying  off  both  toward  the  heart  before  injecting,  and  beyond  injection 
point  after  injecting.     See  addresses  of  firms  selling  injection  syringes,  etc. 

Page  148.  —  Circulation  may  be  shown  as  follows :  Bore  a  hole  one- 
half  inch  in  diameter  through  one  end  of  a  piece  of  thin,  softwood  board. 
The  cover  of  an  ordinary  chalk  box  will  serve.  Etherize  a  frog  till  wholly 
unconscious ;  wrap  it  in  cheesecloth  (to  aid  in  handling)  except  one  hind 
leg.  Bind  the  frog  to  the  board,  letting  the  web  of  the  free  foot  lie  over 
the  hole.  Pin  out  the  web  so  that  it  will  be  lightly  stretched  over  the 
hole,  and  then  place  on  stage  of  compound  microscope,  so  that  light  will 
shine  through  the  web.  Capillaries  of  various  sizes  will  be  seen,  with 
blood  flowing  in  them. 

Page  149.  —  These  large  blood  vessels  have  probably  been  seen  in 
the  course  of  the  demonstration  for  page  137,  but  can  be  further  shown 
by  use  of  a  model  of  the  heart. 

Page  151.  —  Prepared  sections  of  arteries  and  veins  should  be  shown 
under  the  microscope. 

CHAPTER  XI 


I 


Page  155.  —  Arrange  a  rubber  tube  in  horizontal  position,  with  a 
capillary  glass  tube  in  one  end  and  syringe  bulb  at  the  other.  In  the 
middle  of  the  tube  insert  a  glass  T,  and  from  this  side  branch  let  a  glass 
tube  lead  vertically ;  its  upper  end  should  be  open.  On  pumping  in  water 
with  the  syringe  the  pressure  will  be  evident  from  the  height  to  which 
water  rises  in  the  vertical  branch.  If  the  capillary  at  the  end  of  the  hori- 
zontal tube  be  removed,  scarcely  any  pressure  will  be  produced. 


410 


ADVANCED  PHYSIOLOGY 


Page  156.  —  The  conditions  described  here  can  be  imitated  by  using  the 
same  apparatus  as  above,  connecting  a  U-tube  on  the  side  branch,  and 
fining  it  half  full  of  mercury.  The  open  end  of  the  U-tube  should  be  long 
enough  so  that  subsequent  rise  of  the  mercury  during  the  pressure  on  the 
syringe  bulb  will  not  throw  the  mercury  out.  All  air  must  be  taken  out 
of  the  tubes  between  the  water  and  mercury,  as  such  an  air  cushion  will 
practically  counteract  the  effect  of  rhythmical  pressure  on  the  water. 
The  capillary  end  must  be  used  on  the  horizontal  tube  in  this  experiment. 

Page  157.  —  Connect  a  syringe  bulb  with  a  Y-tube,  and  to  the  branches 
of  the  Y  connect  a  glass  and  a  rubber  tube  respectively ;  these  should  be 
of  equal  caliber  and  about  four  feet  long;  the  rubber  tubing  should  be 
thin  and  elastic.  A  removable  glass  capillary  should  be  fitted  to  the 
free  end  of  each  tube.  By  having  a  clamp,  or  valve,  in  each  tube  near 
the  arms  of  the  Y,  water  can  be  sent  through  either  tube  separately.  A 
continuous  stream  can  be  obtained  when  the  bulb  is  pressed  rhythmically, 
only  when  water  is  running  through  the  rubber  tube  and  then  only  when 
the  capillary  is  attached  to  it.     See  figure  below. 


'Rubber 


Glass 


Page  170.  —  It  will  add  to  the  interest  of  the  class  to  show  them  thyroid 
tablets,  adrenaUn  tablets,  and  powdered  pancreatin  such  as  is  used  medici- 
nally and  obtainable  at  any  drug  store,  or  from  physicians. 

Page  172.  —  The  ready  combination  of  oxygen  with  carbon  in  wood  is 
strikingly  shown  by  making  oxygen  and  thrusting  into  it  a  glowing  splinter. 
Fine  wire  taken  from  a  piece  of  picture  cord,  loaded  with  a  bit  of  flaming 
sulfur,  will  burn  if  plunged  into  a  jar  of  oxygen. 


CHAPTER  XII 

Page  178.  —  If  a  large  class  is  being  taught,  the  trachea  and  lungs  of  a 
sheep  or  calf  should  be  used  to  show  the  structure  of  those  organs.  In 
the  case  of  a  small  class  it  is  better  to  show  these  organs  in  position  m  a 
cat;  the  glottis,  epiglottis  and  voice-box,  as  well  as  the  arrangement  of 
the  lungs  in  the  thoracic  cavity,  can  be  shown  in  such  a  small  animal  to 
advantage.  The  lungs  should  be  inflated  by  inserting  a  tube  into  the 
trachea  aud  blowing  them  full  gf  air.   The  bronchi  aud  bronchioles  can  be 


LASOMTORY  l:3tERCl§T3S 


411 


dissected  readily.     A  prepared  section  of  an  injected  lung  should  be  shown 
under  the  microscope. 

Page  179.  —  The  moving  of  particles  of  cork  or  bits  of  wood,  etc.,  by- 
cilia  may  be  shown  by  pithing  a  frog,  cutting  away  the  lower  jaw,  and 
then,  with  the  frog  on  its  back,  putting  such  particles  on  the  roof  of  the 
mouth.  If  this  be  kept  moist  with  0.6%  salt  solution,  these  bits  of  mate- 
rial may  be  slowly  but  visibly  moved  backward  to  the  opening  of  the  gullet. 

In  pithing  a  frog  the  brain  is  destroyed,  and  thus  consciousness  of  any 
pain,  while  the  rest  of  the  body  is  left  entirely  uninjured.  Hold  the  frog 
in  one  hand,  ventral  side  against  the  palm ;  put  the  first  finger  over  top  of 
head  and  hold  against  middle  finger  which,  with  the  other  two,  grasps  the 
body  of  the  frog.  With  the  back  side  of  the  blade  of  a  scalpel  placed 
transversely  to  the  skull,  find  the  groove  between  the  skull  itself  and  the 
first  vertebra.  Drive  the  point  of  the  scalpel  into  this  groove  and  sever 
the  cord ;  then  thrust  a  needle  forward  through  the  foramen  magnum  into 
the  brain  box  and  mix  up  the  brain.  In  this  condition  the  frog  may  give 
reflex  movements,  but  these  are  from  the  cord  alone.  If  it  is  desired  to 
do  away  with  these  also,  pass  a  long  needle  or  stiff  wire  backward  from  the 
wound  through  the  neural  canal  of  the  spine. 

Page  183.  —  Prepared  slides  of  many  forms  of  pathogenic  (disease 
causing)  bacteria  can  be  obtained  from  dealers  in  same,  and  will  greatly 
interest  a  class  if  shown  under  highest  powers  of  the  microscope. 


CHAPTER  XIII 

Page  191.  —  Prepare  the  piece  of  apparatus  shown  in  figure  below. 
By  the  use  of  rubber  bands  as  shown,  demonstrate  to  the  class  how  the 
internal  and  external  intercostals  raise  and  lower  the  ribs,  and  thus  in- 
crease and  decrease  the  size  of  the  thorax. 


412  ADVANCED  PHYSIOLOGY 

Page  193.  —  Arrange  a  bell  jar  of  the  type  shown  In  Figure  102;  or 
let  the  long  stem  of  a  Y-tube  pass  through  the  cork  and  represent  the 
trachea,  the  two  short  branches  representing  the  bronchi.  Attach  to 
each  "  bronchus  "  a  small  rubber  bulb,  such  as  is  on  the  mouth-piece  affair 
used  by  small  boys  as  a  "  squawker."  Close  the  lower  end  of  the  bell 
jar  with  a  sheet  of  rubber  (obtainable  from  any  dentist).  By  pushing  the 
rubber  "  diaphragm  "  upward,  its  position  when  the  breath  is  expelled 
is  imitated,  and  the  "  lungs  "  collapse ;  when  drawn  down,  air  fills  the 
"  lungs."  The  leakages  around  the  cork  can  be  stopped  by  use  of  melted 
paraffin. 

Page  197.  —  The  capacity  of  the  lungs,  amounts  of  tidal  air,  comple- 
mental  air,  etc.,  can  be  effectually  shown  by  use  of  thin  wooden  or  paste- 
board boxes  of  sizes  to  represent  the  different  volumes  referred  to. 

Page  201.  —  Show  changes  in  air  enumerated  here  as  follows : 
a.  With  air  pump,  syringe  bulb,  or  bicycle  pump,  force  the  ordinary  air 
of  the  room  through  a  large  test  tube  of  limewater,  by  conducting  the  air 
through  a  tube  to  bottom  of  water  so  that  the  bubbles  rise  through  it. 

6.  With  a  glass  tube  in  the  mouth  blow  through  limewater.  The  cal- 
cium carbonate  formed  can  be  dissolved  with  a  little  hydrochloric  acid. 

c.  Breathe  on  the  thermometer  bulb. 

d.  Moisture  is  left  on  clean,  cold  glass  when  it  is  breathed  upon. 

e.  Exhale  through  a  glass  tube  into  strong  sulfuric  acid  for  some  time ; 
the  acid  turns  black  on  account  of  organic  matter  in  the  breath.  Extreme 
care  should  be  taken  not  to  draw  the  acid  into  the  mouth. 

Page  205.  —  That  COo  is  heavy  and  will  not  support  combustion  can 
be  shown  by  leading  that  gas  from  a  generator  into  the  bottom  of  a  pint 
fruit  jar,  for  instance ;  it  will  drive  out  the  air  by  collecting  under  it,  thus 
showing  its  weight.  A  lighted  splinter  thrust  into  it  will  go  out.  If  a 
piece  of  candle  be  placed  in  the  bottom  of  a  beaker  and  lighted,  CO2  can 
be  poured  into  the  beaker  and  the  flame  extinguished.  See  Appendix 
list  of  formulae  and  methods. 

Page  206.  —  To  prove  the  fact  of  adjustment  of  breathing  to  different 
circumstances,  have  students  count  rate  of  breathing  when  quietly  sitting, 
just  after  running  up  stairs  and  back,  and  before  getting  up  in  the  morning. 
Averages  struck  from  a  large  number  of  such  reports  will  be  interesting. 

Page  210.  —  If  possible,  the  larynx  of  a  sheep,  calf,  or  dog  should  be 
shown  and  dissected.  This  organ  in  a  smaller  animal  is  not  large  enough  to 
be  of  any  value.  Models  of  this  organ  can  be  bought  (see  list  of  dealers  in 
models)  or  one   may   be   made   from    modeling   wax,  or   carved   from  a 


LABORATORY  EXERCISES  413 

piece  of  hard  soap.     See  list  of  dealers  for  source  of  modeling  wax ;   such 
material  is  often  used  in  grade  schools  or  kindergartens. 

Page  214.  —  Use  can  be  made  here  of  a  tuning  fork.  If  it  is  struck 
and  the  stem  of  it  placed  on  the  side  of  a  hollow  wooden  box  open  at  one 
end  (or  on  a  regular  resonator),  the  combined  effect  of  the  vibration  of 
the  tuning  fork  and  of  the  air  chamber  will  be  marked.  The  text  sugges- 
tion of  talking  into  different  sizes  of  air  containers  should  be  carried  out. 

CHAPTER   XIV 

Page  219.  —  The  kidney  of  a  sheep  or  pig  is  best  adapted  to  show 
structure;  that  of  calf  or  beef  is  not  similarlj^  constructed.  Show  the 
capsule  about  the  kidney,  and  then  split  it  open  by  cutting  from  the 
[convex  side  toward  the  ureter.  The  cortex  and  medullary  regions,  pyra- 
mids, etc.,  are  readily  noted. 

By  use  of  a  cat,  or  rabbit,  the  ureters,  bladder,  and  urethra  can  be 
plainly  demonstrated. 

Page  221.  —  Prepared  slides  of  injected  kidney  should  be  examined 
and  Malpighian  capsules  containing  glomeruli  noted.  The  tubules  will 
be  seen  in  cross  and  longitudinal  section,  though  none  will  be  found  com- 
iplete. 

CHAPTER   XV 

Page  228.  —  Prepared  slides  of  skin  show  practically  all  the  points 
mentioned.  A  student  should  prove  that  a  needle  thrust  into  the  epider- 
mis causes  no  pain  or  bleeding. 

The  subcutaneous  tissue  holding  the  skin  to  the  outer  muscle  layers 
of  the  body  is  easily  demonstrable  in  any  small  animal,  e.g.  cat,  rat, 
white  mice,  or  any  which  may  be  obtainable. 

Page  235.  —  Examine  the  skin  with  a  simple  magnifier  and  compare 
the  markings  of  different  fingers.  Let  one  pupil  be  blindfolded  and  various 
parts  of  his  skin  tested  with  points  of  dividers.  Scissors,  firmly  gripped, 
may  very  well  be  used  in  same  way.  Determine  how  near  together  they 
may  be  and  yet  be  felt  as  two.  Test  the  fingers,  the  back  of  the  hand, 
the  arm,  the  forehead,  and  back  of  the  neck. 

The  determination  of  hot  and  cold  spots  requires  too  much  apparatus 
for  class  use.  However,  interesting  results  are  secured  in  the  following 
manner :  Have  at  hand  two  bowls,  one  containing  quite  warm  water,  the 
other  cool  water.  Put  finger  of  one  hand  into  the  warm  water,  a  finger 
of  other  hand  into  the  cool  water.  Is  there  a  difference  in  sensations  ? 
After  holding  thus  for  a.  minute,  place  both  in  lukewarm  water ;  what 
is  the  result?     Try  to  explain  why. 


414  ADVANCED  PHYSIOLOGY 

Page  236.  —  1.  If  one  holds  the  hand  very  near  a  piece  of  cold  glass, 
e.g.  the  window  glass,  moisture  collects  on  the  latter.  This  is  insensible 
perspiration. 

When  the  opportunity  presents  itself,  each  student  should  very  carefully 
weigh  himself,  follow  this  with  very  vigorous  exercise  during  which  per- 
spiration is  sensibly  produced,  and  then  weigh  himself  again.  The  amount 
of  loss  will  be  the  amount  perspired,  most  of  which  was  sensible  perspira- 
tion. 

2.  The  arrangement  of  the  dermal  papillae  in  rows,  resulting  in  the  fine 
parallel  lines  on  the  hand,  with  special  patterns  particularly  well  seen 
on  the  finger  and  thumb  tips,  is  emphasized  by  use  of  a  hand  lens ;  the 
sweat  glands  open  along  the  tops  of  these  ridges.  A  class  would  be  much 
interested  in  making  a  series  of  "  finger  prints,"  obtained  simply  by  press- 
ing the  finger  or  thumb  tip  on  to  a  paper  or  glass  which  has  been  smoked 
in  gas  or  camphor  flame. 

Page  242.  —  Wet  the  finger  and  blow  upon  it  gently.  In  spite  of  the 
fact  that  the  breath  is  warm,  it  will  feel  cool.  This  is  because  the  air 
current  evaporates  the  water,  and  this  uses  up  the  heat  of  the  finger. 

CHAPTER  XVI 

Page  250.  —  Throughout  this  study  of  the  bones  constant  use  should 
be  made  of  a  good  human  skeleton  and  of  as  many  separate  bones  as  can 
be  procured.  Interesting  comparisons  can  be  made  with  the  skeletons  of 
the  fish,  frog,  and  bird. 

Page  254.  —  A  disarticulated  skull,  like  that  shown  in  Figure  125,  should 
be  on  hand  for  examination. 

Page  260.  —  A  fresh  bone  of  some  size,  e.g.  the  humerus  or  femur 
of  a  sheep  or  calf,  should  be  examined  in  class.  Cross  and  longitudinal 
sections  made  with  hand  saw  show  essential  structure.  Dried  bones  do 
not  show  periosteum  or  marrow  to  advantage. 

Rib  bones  of  a  sheep  or  pig  show  bone  composition  well.  Either  burn 
in  fire  to  remove  animal  matter,  or  place  in  hydrochloric  acid  (15-20%) 
to  remove  mineral  matter. 

Page  262.  —  Microscopic  sections  of  bone,  cross  and  longitudinal,  should 
be  shown  through  medium  powers  of  compound  microscope. 

Page  264.  —  Any  fresh  bone  from  a  joint  is  good  for  showing  carti- 
lage. Microscopic  sections  can  be  conveniently  made  from  fresh  material 
(end  of  femur  of  frog,  if  none  other  is  at  hand)  with  hand  razor ;  mount  on 
slide  in  water  or  1%  acetic  acid. 


LABORATORY  EXERCISES 


415 


Page  265.  —  The  leg  of  a  sheep  or  pig,  with  muscles  removed,  is  good 
for  showing  essential  features  of  a  joint.     An  articulated  human  skele-  , 
ton  should  be  referred  to  constantly  in  connection  with  discussion  of  various 
sorts  of  joints. 

Page  271.  —  In  discussing  and  illustrating  the  matter  of  shoes,  reference 
may  well  be  made  to  the  Munson  last,  after  which  pattern  all  U.  S.  Army 
shoes  are  made.  Aside  from  allowing  plenty  of  room  for  the  small  toes, 
the  inner  side  of  the  shoe  should  be 
so  shaped  that  a  line  drawn  lengthwise 
through  the  middle  of  the  big  toe  and 
continued  backward  will  pass  through 
the  middle  of  the  heel.  Plenty  of  space 
in  front  of  the  toes  is  also  provided. 

The  endeavor  to  make  the  foot  seem 
short  and  small  by  wearing  high  heels 
can  be  shown  by  the  use  of  board 
drawings.  The  following  line  drawings 
are  easily  made : 


Line  A-B  =  apparent  length  of  foot. 
Line  A-C= actual  length  of  foot. 


The  lines  should  pass  through  the  long, 
mid-axes  of  the  big  toes  and  the  middle 
of  the  heels. 


CHAPTER  XVII 

*Page  276.  —  Preparations  of  striped  muscle  make  satisfactory  material 
under  high  powers  of  the  microscope.  If  fresh  muscle  can  be  separated 
into  fine  enough  shreds,  striae  show  fairly  well.     Muscles  of  an  insect. 

I  e.g.  grasshopper,  are  especially  good  for  this.  If  a  section  of  tongue  is 
available,  it  can  be  used  in  this  connection ;  the  muscle  fibers  running  in 
different  directions  are  strongly  striped. 


416 


ADVANCED  PHYSIOLOGY 


Page  278.  —  To  show  the  relation  of  muscle  to  nerve,  tetanus,  etc., 
destroy  the  brain  of  a  frog,  remove  the  skin  of  the  upper  part  of  the  hind 
leg,  and  by  pulling  apart  the  muscles  locate  the  large  sciatic  nerve.  By 
stimulating  the  nerve  the  muscles  of  the  leg  will  contract.  For  more 
careful  study  proceed  as  follows :  Follow  the  nerve  carefully  without 
stretching  or  even  touching  it  any  more  than  necessary  through  the  hip 
joint  to  its  exit  from  the  spinal  cord  in  the  middle  of  the  back;  cut  it 
there,  carefully  get  it  free  from  the  surrounding  tissues,  and  coil  it  up 
(two  inches  or  so  in  length)  on  the  muscle  at  the  knee  joint.  Do  not  allow 
it  to  lie  on  the  skin  of  the  lower  leg.  Now  remove  the  muscles  from  the 
thigh  region,  reserving  the  femur  bone ;  cut  the  latter  off  near  the  hip, 
and  clamp  in  a  holder  supported  on  a  standard.  Place  the  nerve  on  a 
pair  of  electrodes  which  are  connected  with  a  key  and  cells  in  an  electric 
battery  circuit,  taking  care  all  the  time  not  to  let  the  nerve  get  dry ;  mois- 
ten with  0.6%  salt  (NaCl)  solution,  with  camel's  hair  brush.  By  opening 
and  closing  the  key,  a  single  or  often  repeated  stimulus  can  be  sent  into 
the  nerve,  and  the  characteristic  effect  on  the  muscle  noted. 


Figure  showing  simplest  possible  scheme  of  apparatus  for  using 
nerve-muscle  preparation. 
B  =  battery  E  =  electrodes 

K  =  key  iV=  nerve  X  A  T 

w  =  circuit  wires  Af  =  muscle  W 

PF=  weight 


Pi^e  281.  —  Microscopic  preparations  of  smooth  muscle  which  have 
been  properly  stained  are  most  satisfactory  for  examination.  Unless 
there  is  at  hand  special  apparatus,  it  is  not  easy  to  show  the  normal  reac- 
tion to  stimuli  of  smooth  muscle.  So,  too,  its  involuntary  rhythmic  con- 
tractions cannot  be  easily  demonstrated  unless,  if  taken  from  intestine  of 
warm-blooded  animal,  it  be  maintained  at  the  full  body  temperature  in 


LABORATORY  EXERCISES  417 

specially  devised  chamber.     It  is  not  a  practical  experiment  to  attempt 
with  limited  time  and  apparatus. 

Page  282.  —  To  try  out  the  point  that  heart  muscle  is  apparently  not 
susceptible  of  tetanus,  lay  bare  the  heart  of  a  frog  of  which  the  brain  is 
destroyed,  and  bend  the  electrodes  of  such  an  apparatus  as  is  shown  on 
opposite  page  so  that  the  heart  may  be  placed  between  them.  Rapid 
making  and  breaking  of  the  current  can  then  be  secured  by  use  of  the  key. 

CHAPTER  XVIII 

Page  290.  —  The  bones  of  the  head  of  a  cat  are  sufficiently  thin  so 
that  they  dissect  easily.  The  brain  coverings,  fluids  present,  main  divi- 
sions of  the  brain,  and  distribution  of  blood  vessels  can  be  admirably 
shown  in  such  a  dissection.  If  it  is  desired  to  show  the  distribution  of 
gray  and  white  matter,  take  such  a  brain  (or  preferably  that  of  a  sheep) 
and  wrap  it  in  cotton  to  prevent  flattening  against  side  of  jar,  and  place 
for  two  weeks  or  so  in  potassium  bichromate  solution  (see  Formula  10). 
Sections  can  then  be  made  through  it  with  a  razor  and  internal  structures 
shown  to  any  desired  extent.  The  brain  can  be  hardened  immediately 
in  formalin  (5%),  but  will  not  show  above  differentiation. 

While  the  brains  of  fishes  have  their  parts  developed  to  sizes  which  differ 
from  those  of  the  cat's  brain,  their  general  relations  and  order  of  arrange- 
ment are  the  same.  The  cartilage  skull  of  the  shore  dogfish  (Mustelus  or 
Squalus)  permits  very  easy  and  beautiful  demonstration  of  all  brain  parts 
and  nerves.     See  address  Ust  of  dealers. 

Page  293.  —  In  order  to  demonstrate  the  so-called  gray  and  white 
regions  of  the  central  nervous  system,  the  parts  must  be  prepared  in  spe- 
cific ways.  See  formula  for  this  purpose.  Even  free-hand  sections  of  such 
material  make  clear  demonstrations. 

Page  294.  —  Prepared  sections  of  the  cortex  of  the  brain  show  cells 
well,  though  the  student  will  get  but  a  limited  idea  of  the  brain  as  a  whole 
from  any  one  section  which  may  be  studied. 

Page  301.  —  The  general  appearance  and  structure  of  the  spinal  cord 
can  be  well  learned  by  obtaining  at  a  market  a  piece  of  the  spinal  cord  of 
some  animal  {e.g.  the  sheep  or  ox)  still  in  its  coverings.  If  this  is  hardened 
in  equal  parts  of  5%  formalin  and  70%  alcohol,  it  is  easily  handled.  If  the 
potassium  bichromate  method  is  followed  the  results  will  be  better  yet. 

Prepared  sections  of  the  spinal  cord  will  also  be  interesting. 

Page  302.  —  That  the  cord  is  the  path  through  which  nerve  impulses 
are  sent  out  from  the  brain  can  be  shown  on  the  body  of  a  freshly  beheaded 


418  ADVANCED  PHYSIOLOGY 

frog.  If  electrodes  are  pliced  on  the  exposed  anterior  end  of  the  cord, 
and  a  stimulus  given  from  a  battery  current,  or  from  an  induction  coil, 
the  effect  on  the  whole  posterior  part  of  the  body  will  prove  that  the  cord 
is  the  conductor  of  the  shock.  The  above  method  is  the  neatest;  but 
essentially  the  same  result  is  obtained  by  probing  the  exposed  cord  with 
a  needle. 

Page  305.  —  Spinal  nerves  can  be  easily  shown  by  removing  the  organs 
in  the  body  cavity  of  a  frog,  after  which  the  spinal  nerves,  including  the 
brachial  and  lumbar  plexuses,  show  without  further  dissection.  Their 
number  is  less  than  in  man,  being  ten  only ;  it  will  also  be  easy  to  notice 
that  two  go  to  the  arm  (fore-foot)  and  are  called  the  brachial  plexus. 
Four  pass  to  the  hind  leg,  and  together  are  called  the  sciatic  plexus.  The 
same  terms  are  used  in  human  anatomy. 

Page  307.  —  The  features  of  a  nerve  fiber  as  described  here  can  be  made 
out  by  separating  a  spinal  nerve  of  a  frog  into  its  component  fibers,  and 
mounting  them  on  a  slide  in  salt  solution  under  the  microscope. 

CHAPTER  XIX 

Page  314.  —  Simple  reflexes  may  be  shown  upon  a  frog  whose  head  has 
been  removed  or  whose  brain  is  destroyed.  The  latter  method  is  neater, 
while  the  former  more  evidently  shows  that  the  brain  is  absent.  Suspend 
the  frog  so  that  its  body  hangs  downward,  and  then  gently  pinch  the  toe 
or  dip  it  into  weak  hydrochloric  acid. 

Touch  a  minute  spot  on  the  flank  with  strong  acid  and  note  that  the 
hind  leg  will  scratch  it  even  with  brain  lacking.  This  weU  illustrates  a 
spinal  reflex. 

Page  324.  —  The  main  components  of  the  sympathetic  system  of 
nerves  in  a  large  frog  show  quite  clearly  as  soon  as  the  digestive  tract  and 
reproductive  organs  are  carefully  removed.  Do  not  tear  out  the  mesen- 
teries or  the  sympathetic  chain  will  probably  be  ruined.  It  is  delicate 
but  appears  lying  parallel  to  the  back-bone,  some  of  the  way  against  it. 
The  sympathetic  system  can  be  better  shown  in  a  cat  if  dissected  by  a 
person  knowing  the  anatomy  well. 

CHAPTER  XXI 

Page  340.  —  The  parts  of  the  eye  mentioned  in  the  next  few  paragraphs 
can  be  best  shown  in  a  model :  the  external  muscles  are  generally  shown 
on  the  head  of  a  manikin. 

Have  pupils  note  how  rapidly  the  muscles  closing  the  eyes  operate; 
only  about  .05  of  a  second  is  required  to  close  the  lid. 


LABORATORY  EXERCISES  419 

Page  341.  —  The  muscles  which  move  the  eye  can  be  well  shown 
by  use  of  the  eye  of  a  dog-fish.  The  skull  is  cartilaginous  and  easily  cut 
away,  and  the  muscles  are  diagrammatically  plain.  The  nerves  control- 
ling them  can  also  be  identified  if  sufficient  care  is  taken. 

Page  343.  —  The  eye  of  an  ox  can  be  easily  dissected  to  show  practi- 
cally all  the  parts  mentioned  here.  In  taking  off  the  choroid  coat  the 
pigment  layer  of  the  retina  usually  comes  away  also,  but  the  cell  layers 
will  be  left  in  position.     Material  should  be  perfectly  fresh. 

Page  344.  —  Let  one  student  face  a  bright  light  while  keeping  one  eye 
covered  with  the  hand;  others  should  notice  difference  in  size  of  pupils 
when  the  hand  is  removed.     This  makes  clear  the  function  of  the  iris. 

Page  348.  —  1.  A  very  convincing  way  of  showing  the  image  on  the  retina 
to  be  inverted  is  to  mount  the  perfectly  fresh  eye  of  a  chloroformed  albino 
rabbit  in  one  end  of  a  stiff  paper  tube,  the  cornea  looking  outward.  A 
person  looking  through  the  tube  at  the  back  of  the  eye  sees  the  inverted 
image  of  whatever  is  in  front  of  it.  Always  look  at  something  brightly 
illuminated,  e.g.  anything  out  of  doors  on  a  sunny  day,  or  an  electric 
bulb,  or  candle  flame. 

2.  A  great  many  of  the  principles  involved  in  the  passage  of  light  into 
the  eye  can  be  well  shown  by  use  of  an  artificial  eye  apparatus.  The 
ordinary  defects  in  the  eye,  as  well  as  their  correction,  can  also  be  shown 
with  it.  Ordinary  loose  lenses  can  also  be  used  as  shown  in  the  diagrams  ; 
the  source  of  the  light  should  be  confined  in  a  dark  box,  with  a  single  hole 
in  its  side,  through  which  light  rays  can  emerge  and  strike  the  lenses. 
A  darkened  room  is  imperative  for  all  experimental  work  with  light. 

Permanent  models  of  lenses  and  rays  of  light  can  easily  be  made.  A 
lens  of  any  shape,  regular  or  deformed,  can  be  made  of  modeUng  wax. 
This  can  be  supported  on  brass  rods  above  the  middle  of  a  board  base. 
The  source  of  light  can  be  represented  by  a  point  on  an  upright  piece  of 
wood  a  foot  or  two  from  the  lens,  and  the  retina  by  a  flat  piece  of  board  a 
foot  or  two  from  the  other  side  of  the  lens.  String  or  thread  can  be  used 
as  rays  of  light,  and  strung  from  source  of  light  to  lens,  where  they  can  be 
fastened  with  pins  as  the  wax  is  soft.  The  exit  of  rays  on  the  other  side 
can  be  set  up  in  a  similar  way,  and  their  distribution  on  the  retina  shown 
by  fastening  the  "  rays  "  with  tacks. 

Page  361.  —  Adaptation  of  the  eyes  to  different  distances  is  easily 
felt  by  the  pupil  if  he  holds  up  a  finger  of  one  hand  about  a  foot  from  his 
eyes,  with  finger  of  other  hand  in  same  line  two  feet  away.  Give  atten- 
tion first  to  one  and  then  to  the  other.    Board  diagrams  of  what  happens 


420  ADVANCED  PHYSIOLOGY 

in  changing  the  angle  of  convergence  of  light  entering  the  pupil  will  assist 
in  making  the  facts  clear. 

Page  353.  —  If  possible,  arrange  with  some  ociihst,  or  physician  with 
a  knowledge  of  optics  and  of  eye  troubles,  to  bring  into  class  pieces  of 
testing  apparatus  and  charts  and  to  explain  the  commoner  eye  defects 
and  method  of  correction. 

Page  355.  —  Prepared  sections  of  the  retina  will  prove  very  fascinat- 
ing if  shown  in  this  discussion,  not  for  comment  on  its  details,  but  in 
proof  that  it  is  a  comphcated,  delicate  structure. 

Page  358.  —  Sets  of  differently  colored  worsted  yarns  can  be  obtained 
for  testing  for  color-blindness.  Require  pupils  to  place  together  such 
samples  as  seem  to  be  of  the  same  color.  It  is  quite  probable  that  some 
student  will  show  defective  color  vision. 

CHAPTER  XXII 

Page  362.  —  A  large  model  of  the  entire  ear  must  be  on  hand  in  order 
that  the  student  may  get  a  clear  idea  of  it.  A  separate  preparation  of 
the  temporal  bone  of  the  human  skull,  sawed  open  to  show  the  ear  struc- 
tures, is  also  desirable. 

Page  366.  —  In  no  other  animal  can  the  semicircular  canals  be  so  well 
shown  as  in  the  dog-fish,  in  which  they  occupy  a  large  area  just  back  of  the 
eye  and  can  be  easily  dissected  out  of  the  cartilaginous  skull. 

Page  370.  —  If  stringed  instruments  are  not  at  hand  to  show  sym- 
pathetic vibration,  two  tuning  forks,  vibrating  at  the  same  rate,  can  be 
used.  One  should  be  struck  and  its  stem  placed  upon  a  table  top,  while 
the  other  is  held  near  it.  Then  smother  the  one  struck  and  place  the 
stem  of  the  second  on  the  table  top.  The  second  will  be  found  to  give 
out  sound. 


APPENDIX 

Address  List  of  a  Few  Firms  Dealing  in  Materials  for 
Demonstrations  or  Laboratory  Work 

Zoological  material,  e.g.  dog-fish,  flies,  mosquito  adults  or  larvoe,  etc. : 

(a)  Supply  Department,  Marine  Biological  Laboratory,  Woods  Hole, 
Mass. 

(6)  The  Chicago  Biological  Supply  House,  5505  Kimbark  Avenue, 
Chicago,  111. 

(c)  The  Southern  Biological  Supply  Company,  Natural  History  Building, 
New  Orleans,  La. 

Microscopic  slides: 

(a)  Powers  and  Powers,  Sta.  A,  Lincoln,  Neb. 

(&)  The  Chicago  Biological  Supply  House,  5505  Kimbark  Avenue, 
Chicago,  111. 

(c)   Ward's  Natural  Science  Establishment,  Rochester,  N.  Y. 

{d)  The  Cambridge  Botanical  Supply  Company,  Waverley,  Mass. 

Living  unicellular  animals: 
(a)  Powers  and  Powers,  Sta.  A,  Lincoln,  Neb. 

(6)  The  Chicago  Biological  Supply  House,  5505  Kimbark  Avenue,  Chi- 
cago, 111. 

(c)  Southern  Biological  Supply  Company,  Natural  History  Building, 
New  Orleans,  La. 

(d)  Cambridge  Botanical  Supply  Company,  Waverley,  Mass. 

Microscopes  and  dissecting  instruments: 

(a)  The  Spencer  Lens  Company,  Buffalo,  N.  Y. 

(6)  Bausch  and  Lomb  Optical  Company,  Rochester,  N.  Y. 

(c)  Central  Scientific  Company,  460  East  Ohio  St.,  Chicago,  111. 

{d)  Arthur  H.  Thomas  Company,  Philadelphia,  Pa. 

For  physiological  apparatus: 

(a)  The  Harvard  Apparatus  Company,  Back  Bay  P.  O.,  Boston,  Mass. 

(b)  Wilham  Gaertner  and  Company,  5345  Lake  Avenue,  Chicago,  111. 

For  skeletons  and  models: 

(a)  Ward's  Natural  Science  Establishment,  Rochester,  N.  Y. 

(h)  The  Kny-Scheerer  Company,  404  West  27th  Street,  New  York  City. 

(c)  Charles  H.  Ward,  Rochester,  N.Y. 

421 


422  ADVANCED  PHYSIOLOGY 

Modeling  wax: 

(a)  Any  dealer  in  art  goods. 

(6)  Devoe  and  Reynolds,  Fulton  Street,  New  York  City, 

General  laboratory  supplies,  not  named  above: 

(a)  Arthur  H.  Thomas  Company,  Philadelphia,  Pa. 

(6)  Central  Scientific  Company,  Chicago,  111. 

Formulae  and  Methods  of  Making  Various  Substances 
Mentioned  in  This  Book 

1.  Formula  for  iodine  solution  for  use  in  testing  for  starch : 

4  parts  potassium  iodide 
1     "     iodine 
40     "     water 

Dissolve  above  and  add  960  parts  water.  Smaller  amounts  may  be 
made  using  same  proportions. 

2.  Formula  for  Pasteur's  solution : 

10  parts  potassium  phosphate 
1      "     calcium  phosphate 
1      "     magnesium  sulfate 
50     "     ammonium  tartrate 
750     "     cane  sugar 
4188     "     water 

3.  Formula  for  artificial  gastric  juice : 

0.2    parts  hydrochloric  acid 
0.1       "     pepsin 
0.05     "     calcium  chloride 
0.05     "     potassium  phosphate 
100  "     water 

The  above  is  a  precise  formula,  but  for  ordinary  experiments  for  ele- 
mentary classes  the  calcium  and  potassium  compounds  may  be  omitted  and 
the  other  two  used  in  greater  strength. 

4.  Formula  for  artificial  pancreatic  juice: 

0.6  part  common  salt  0.2  part  pancreatin 

0.2     "   sodium  carbonate  0.2     *'    potassium  phosphate 

0.2     "   diastase  0.2     "    lipase 

100  parts  water 

For  elementary  work  the  potassium,  diastase,  and  lipase  maybe  omitted. 


APPENDIX 


423 


W^O 


H,0 


JVa/k^ 


5.  Formula  for  lime  water : 

Add  calcium  hydrate  to  water  till  saturation  is  reached ;  then  filter. 

6.  Formula  for  normal  salt  solution : 

0.6-0.75%.     This  solution  is  merely  sodium  chloride  in  distilled  water. 

7.  Fehling's  solution  for  sugar  tests : 

A  quantity  sufficient  for  convenient  use  can  be  made  up  as  follows: 
Solution  1 :  dissolve  17  grams  (about  1^  teaspoonfuls)  of  pure  copper  sulfate 
in  100  cc.  (a  quarter  pint)  of  water.  Solution  2  :  dissolve  75  grams  (about 
6  teaspoonfuls)  of  Rochelle  salt  and  25  grams  (about  1^  5-inch  sticks) 
caustic  soda  in  250  cc.  (about  \  pint)  of  water.  Mix  the  two  solutions 
thoroughly.  This  solution  keeps  in  usable  shape  only  for  short  time  and  it 
is  more  convenient  to  procure 
tablets  ready  for  dissolving 
from  a  druggist.  Whether  the 
solution  is  correct  or  not  can 
be  ascertained  by  boiling  a 
little ;  if  it  loses  its  color,  the 
solution  is  useless. 

8.  The  following  is  a  con- 
venient method  of  making 
oxygen  gas : 

Put  some  spdium  peroxid 
powder  into  a  medium  sized 
flask.  This  should  be  fitted 
with  a  rubber  cork,  through 
which  runs  a  glass  tube  for  leading  off  the  gas,  and  a  separatory  funnel 
by  means  of  which  water  can  be  slowly  dropped  on  to  the  peroxid  at  will. 
The  gas  forms  immediately  and  in  large  quantity.     It  can  be  most  easily 

O  collected  in  jars  over  water  by 

^_^  downward    displacement;    see 

figure. 

9.   To  make    carbon  dioxid 


Put  into  a  medium  sized  flask 
some  broken  bits  of  marble. 
Cover  with  water.  Through  the 
rubber  cork  in  the  neck  pass  a 
glass  tube  through  which  to 
lead  off  the  gas ;  also  a  thistle 
tube,  letting  the  lower  eod  qi  the 


\.        ^^^m: 


Illustrating  the  method  of  making  oxygen  gas. 


M&H^O 


Illustrating  the  method  of  making  carbon  dioxid 


424  ADVANCED  PHYSIOLOGY 

latter  reach  below  the  water  level.  Pour  hydrochloric  acid  into  the  thistle 
tube ;  CO2  is  immediately  formed,  though  slowly,  and  can  be  collected  by 
merely  letting  the  gas  run  into  the  bottom  of  a  jar ;  the  weight  of  the  gas 
will  force  out  the  air  above  it.  Too  free  diffusion  into  the  air  should  be 
prevented  by  covering  the  jar  with  a  glass  plate ;  see  figure. 

10.   Formula  for  fluid  in  which  to  preserve  parts  of  central  nervous 
system  so  as  to  show  white  and  gray  regions : 

10  parts  potassium  bichromate 
15-20     "     formaldehyde  (40%) 
500     "     water 

Let  material  stand  in  above  mixture  two  weeks  or  so ;  if  not  hard  then, 
place  overnight  in : 

2  parts  5%  formalin 

1      "     95%  alcohol  (ethyl) 

A  fresh  brain  placed  in  the  last  named  mixture  alone  will  harden  in  two 
days ;  but  the  regions  of  gray  and  white  matter  will  not  be  differentiated. 

Chemical  Composition  of  Various  Substances  Mentioned 
in  This  Book 


Acetic  Acid 

C.H4O. 

Alcohol 

C2H6OH 

Ammonia 

NH3 

Caffein 

05H(CH3)3N40a 

Carbon  Dioxid 

C02 

Fat  (stearin) 

CsvHiioOe 

Glycogen 

CeHioOs 

Glycerin 

C3H5(OH)3 

Hydrochloric  Acid 

HCl 

Milk  Sugar 

C12H22O11 

Proteid  (egg  albumin) 

C204H322O66N52S2 

Starch 

CeHioOa 

Sugar  (grape  sugar, 

glucose, 

etc.) 

CeHizOe 

Urea 

CO(NH2)2 

Uric  Acid 

CaH403N4 

APPENDIX 


425 


A  Comparison   of  the   Units   of  Measure   Commonly  Employed 
in  America  with  Those  of  the  Metric  System 


Length 


Weight 


Capacity     .     . 


Work  .     . 


Heat  .     . 


1  meter  (m.)  =1000  millimeters  (mm.). 
1      "  =100  centimeters  (cm.)  =39.37  inches. 

1  inch  =25.4  millimeters. 

1  foot  =30.5  centimeters. 

.  1  M  =  TojHj  millimeter  =5^055  inch  (nearly). 

1  kilogram  (kg.)  =1000  grama  (g.)  =2.2  lb.  Avoirdupois. 

1  gram  (g.)  =1000  milligrams  (mg.)  =15.4  grains, 

1  pound  (Avoir.)  =453.6  grams,  or  about  5  kilogram. 

1  ounce         "  =28.35  grams  =437.5  grains. 

1  liter  (1.)       =1000  cubic  centimeters  (cc.)  =2.1  pints. 

1  fluid  ounce  =29.57  cubic  centimeters. 

1  pint  =16  fluid  oz.  =473.1  cubic  centimeters. 

1  gallon  =3.78  liters. 

1  cubic  inch  =16.38  cubic  centimeters. 

1  cubic  foot  =28.3  liters. 

1  kilogram-meter  (kg.m.)  =7.23  foot-pounds. 
1  foot-pound  =.138  kilogram-meter. 

1  foot-ton  =276  kilogram-meters. 

1  unit  of  heat        =heat  necessary  to  raise  1  pound  of  water  through 

1°  F. 
1  calorie  (Metric)  =    "  "  "     "      1  gram  "         '* 

1°  C. 
Mechanical  equivalent  of  heat  unit  =778  foot-pounds. 

"  "         "   calorie       =427  gram-meters. 


INDEX 


Abdominal  cavity,  90 
Absorption  of  food,  112,  116 

summary  of  digestion  and,  121 
Accommodation,  process  of,  349 

mechanism  of,  350 
Adenoids,  176 
Adipose  tissue,  228 
Adrenal  bodies,  170 
Ague,  fever  and,  132 
Air  changes  in,during  breathing,200 

and  house  location,  385 

in  lungs,  197 

in  middle  ear,  364 
Albumen,  28 

in  Bright's  disease,  226 
Alcohol  and  brain,  333 

and  length  of  life,  335 

and  indigestion,  108 

as  food,  59 

formation  of,  through  fermenta- 
tion, 62 

influence  of,  on  circulation,  164 

oxidation  of,  in  body,  59 

users  and  railroad  companies,  335 
Alveolus,  of  gland,  81 

of  lung,179 
Amino-acids,  201 
Ampullae  of  ear,  366 
Amylopsin,  103 
Anabolism,  35 
Anatomy,  definition  of,  10 
Anesthetics,  330 
Animals,  multicellular,  23 

unicellular,  22,  23 

warm  and  cold  blooded,  239 
Antiseptic  lotions,  235 
Antitoxin,  86,  287 
Aorta,  141 

Apoplexy — see  Paralysis,  326 
Appendicitis,  110 
Appendix,  vermiform,  106 
Appetite  as  guide  in  eating,  51 
Aqueous  humor,  344 
Arachnoid  fluid,  290,  301 


Arborizations, 

(see  Dendrites) 
Arm,  256 

blood  in,  157 

bones  of,  256 

nerves  to,  305 
Arteries,  main,  in  body,  145,  146 

pulmonary,  139 

structure  of,  151 
Astigmatism,  354 
Auricle,  137 
Axis  cylinder  (axon)  of  nerves,  307 

Backbonej  the,  251 
Bacteria,  67 

and  white  corpuscles,  126 

beneficial,  68 

distribution  of,  68 

harmful,  70 

immunity  against,  71 

in  milk,  393 

multiplication  of,  65 

of  blood  poisoning,  131 

of  diphtheria,  86 

of  pneumonia,  183 

of  tonsilitis,  85 

of  tuberculosis,  184-189 

relation  of,  to  disease,  70 
Ball  and  socket,  267 
Basilar  membrane,  370 
Baths,  cold,  244 

hot,  246 

in  general,  244 
Beans,  40,  47 
Beef,  40,  46 
Beverages,  375 
Bicuspid  teeth,  75 
Bile,  101,  102 
Bladder,  gall,  101 

stones,  226 

urinary,  223 
Bleeding,  156 
Blind  spot,  356 
Blisters,  167,  230 


427 


428 


INDEX 


Blood,  amount  of,  123 

cells,  16,  124,  126 

clotting,  128 

composition  of,  123 

demonstration  of,  406 

diseases  of,  130 

in  excretion,  217 

lack  of,  in  some  animals,  122 

part  played  by,  in  paralysis,  326 

platelets,  127 

poisoning,  131 

pressure,  154 

rate  of  flow  of,  158 

tissue,  13 

vessels,  145 

in  dermis,  233,  241 
in  kidneys,  221    . 
in  lungs,  180 
regulation  of  size  of,  158 
structure  of,  150 
to  legs,  158 
Blushing,  160 
Body,  cavity,  89 

chemical  composition  of,  27,  28 
Boils,  131 
Bone  cells,  15,  261,  263 

composition  of,  260 

material  used  in  making,  53 

repair  of,  261 

structure  of,  259 

tissue,  12,  262 
Bones,  carpal,  257 

dislocation  of,  269 

of  children  and  adults,  260 

of  ear,  3,64 

of  face,  255 

of  feet,  258 

of  jaw,  255 

of  leg  and  hip,  257 

of  skull,  254 

of  spine,  251 

patella,  266 

rib,  253 

setting  of,  262 
Brain,  290-293 

alcohol  and,  333 

care  of,  321 

cortex  of,  293 

demonstration  of,  417 

drugs  affecting,  329 

dura  mater  of,  290 

ventricles  of.  293 


Bread,  composition  of,  46 
proteid  in,  39 

Breathing  and  exercise,  205 

carbon  dioxid,  204 

diaphragm,  192 
Breathing,  habits,  198 

pure  oxygen,  203 

rib,  191 

through  mouth,  174 
Bright's  disease,  226 
Bronchial  tubes,  178 
Bronchitis,  183 
Bunions,  230 
Burns,  248 
Butter,  46 

Caffein,  58.  164 

Calculi  in  bladder,  226 

Callouses,  230 

Calories  produced*  in  a  day,  48 

Canaliculi,  263 

Canals,  external  ear,  362 

semicircular,  366 
Canine  teeth,  75 
Capillaries,  146,  148,  409 

structure  of,  152 
Carbohydrates,  31 

after  absorption,  118 

compared  with  fats,  33 

kinds  of,  31 

per  cent  of,  in  foods,  43 

tests  for,  400 

uses  of,  32 
Carbon  dioxid  and  ventilation,  207 

in  respired  air,  200,  204 

method  of  making,  423 
Cardiac,  muscle,  281 

nerves,  145 

valve,  91 
Carpal  bones,  257 
Cartilage,  12,  263 

ends  of  ribs,  253 

of  larynx,  211 

rings  of  trachea,  177 
Casein,  29 
Cavity  abdominal,  90 

mastoid,  363 

thoracic,  90 


INDEX 


429 


Cell,  definition  of,  19 

division  of,  20 

growth,  20 

repair,  2G 

structure,  17 

theory,  15 

wall,  18 
Cells,  division  of  labor  among,  24 

gland,  16 
Cells,  repair  of,  20 
Cement  of  teeth,  76 
Center,  circulatory,  161 

coordinating,  298 

respiratory,  194 
Cereals,  composition  of,  47 
Cerebellum,  291 

functions  of,  298 

structure  of,  297 
Cerebrum,  291 

functions  of,  295 

localization  in,  296 

structure  of,  294 
Charity    Organization    Society    of 
New  York,  rules  of,  as  to  tuber- 
culosis, 187 
Cheese,  39,  46 
Chemical  compounds,  28 
Chills,  132 

Chordae  tendinae,  139 
Choroid,  344 
Chyle,  105 
Chyme,  97 
Cilia,  in  Eustachian  tubes,  364 

demonstration  of,  411 

in  nose,  174 

in  pharynx,  84 

in  trachea,  179 

movement  of,  403 
CUiary  muscle,  351 
Circulation,  apparatus  illustrating, 
408;  diseases  of,  153 

importance  of  vigor  of,  161 

influence  of  drugs  on,  164 

influence  of  heat  and  cold,  162 

pulmonary,  140,  141,  150 

summary  of,  150 

systemic,  147,  150 
Clavicle,  256 

Cleaning  of  buildings,  388 
Clothing,  246 

and  colds,  182 


Clotting,  of  blood,  128 

purpose  of,  130 
Coccyx,  253 
Cochlea,  366 
Coecum,  105 
Coelomic  fluid,  90 
Coffee,  58,  330 
Cold  baths,  244 

influence  of,  on  circulation,  162 

nerve  endings  perceiving,  234 

rigor  of  muscle,  279 
Colds,  181 
Colloids,  116 
Collagen,  260 
Colon,  105 
Color  blindness,  359 

vision,  358 
Condiments,  52 
Cones  in  retina,  355 
Confectionery,  48 
Conjunctiva  of  eye,  343 
Connective  tissue,  12,  15,  276 
Constipation,  106 
Consumption,  184,  381 
Cooking,  53 

relation    of,    to    digestibility    of 

food,  55 
Coordination,  298 
Cornea,  343 
Corns,  230 
Corpus  callosum,  293 
Corpuscles,  nerve  ending,  309 

red  blood,  124 

white,  126 
Cortex  of  brain,  293 

of  hair,  231 

of  kidney,  220 
Cramming,  323 
Cranium,  254,  290 
Cretinism,  170 
Crura  cerebri,  291 
Crystalloids,  116 
Cystic  duct,  101 

Dandruff,  230 
Deafness,  372 
Deficiency  diseases,  45 
Dendrites,  294,  310 
Dentine,  76 
Dermis,  228,  233 
papillae  of,  234 
Diabetes,  226 


430 


INDEX 


Diaphragm,  location  and  structure 
of,  89 

manner  of  functioning,  193 

nerves  to,  195 
Diastole,  141 
Digestion,  in  general,  74 

in  intestine,  101 

in  mouth,  80 

in  stomach,  93 

summary  of,  121 
Digestive  system,  74,  88,  98 
Diphtheria,  71,  86,  380 
Diseases,  associated  with  blood,  130, 

163 
Diseases,  hip,  185,  287 

of  blood,  130 

of  excretory  organs,  225 

of  intestinal  tract,  109 

of  mastoid  cavities,  364 

of  mouth  and  throat,  85,  176 

of  muscles  and  bones,  287 

of  nervous  system,  325 

of  respiratory  system,  181 

of  thyroid  glands,  170 

relation  of,  to  imagination,  323 

struggle  against  germs  of,  328 
Disinfection,  73 
Dislocation  of  bones,  269 
Division  of  cells,  20 

of  labor  in  body,  24 
Dropsy,  167 
Drowning,  209 
Drugs,  164 

affecting  brain,  333 
Drum,  ear,  362 
Duct,  cystic,  101 

hepatic,  101 

pancreatic,  102 

salivary,  81 

thoracic,  120 
Ductless  glands,  168 
Duodenum,  100 
Dura  mater,  of  brain,  290 

of  cord,  301 

Ear,  362-365 

air  in  middle,  364 

ampullae  of,  366 
Eggs,  39,  46, 
Elements,  chemical,in  living  matter, 

25,27 
Emulsion  of  fats,  104 


Enamel  of  teeth,  76 

Endolymph,  366 

Energy,  carbohydrate  sources  of,  32 

fat  sources  of,  32 

proteid  sources  of,  30 
Enunciation,  215 
Enzymes,  63 
Epidemics,  395 
Epidermis,  228 
Epiglottis,  85 
Epithelium,  12,  15 
Ethmoid  bone,  175 
Eustachian  tubes,  363,  372 

and  deafness,  84 
Excretion,  of  urea,  218,  221 

organs  of,  216 

through  skin,  235 
Exercise,  and  breathing,  205 

for  student,  285 

kinds  of,  285 

need  of,  284 

walking  as,  285 
Expiration,  192 
Eye,  340 

apparatus  illustrating,  418 

conjunctiva  of,  343 

formation  of  images  in,  345 
Eyelids,  340 
Eyesight,  354 

Faeces,  107 
Fainting,  163 
Farsightedness,  353 
Fat,  after  absorption,  119 

as  body  component,  28 

cells,  16 

characteristics  of,  45 

comparison  with  carbohydrates, 
33 

kinds  and  distribution  of,  32 

per  cent  of,  in  common  foods,  44 

tests  for,  401 

tissue,  13 
Fatigue,  279 
Fats,  carbohydrates  compared  with, 

34 
Feet,  bones  of,  258 

care  of,  269 

defective,  270 
Fehling's  solution,  423 
Femur,  258 


INDEX 


431 


Fermentation,  alcoholic,  62 

of  starch,  62 

demonstration  of,  402 
Ferments,  characteristics  of,  64 

kinds  formed  in  the  body,  65 

organized,  63 

unorganized,  63 
Fever,  and  ague,  132 

scarlet,  71 

typhoid,  71,  110 

yellow,  134 
Fibres,  muscle,  275 

nerve,  307 
Fibrin,  129 

ferment,  129 
Fibrinogen,  129 
Fibula,  258 
Finger  nails,  233 
Fingers,  bones  of,  257 
Flatfoot,  271,  272 
Flavorings,  53 
Flour,  39 
Fluid,  arachnoid,  290,  301 

synovial,  265 
Focus  of  light,  347 
Food,  absorption  of,  112,  116 

alcohol  as,  59 

amount  needed,  48 

changes  in,  after  absorption,  117 

composition  of  common,  46 

digestion  and  absorption  of,  121 

habits,  37 

inspectors,  393 

parasites  in,  55 

predigested,  96 

purity  of,  393 

relation  of,  to  work,  98 

salt  in,  53 

supplies,  sanitary  handling,  393 

value  of,  38 
Foramen,  magnum,  290 

ovale,  363 

rotundum,  363 
Form  of  body,  factors  influencing, 

260,  285 
Fovea  centralis,  356 
Frostbites,  248 
Furnishings,  hygienic,  388 

Gall  bladder,  101 
Ganglion,  spinal,  305 
sympathetic,  324 


Garbage  disposal,  394 
Gastric,  glands,  92 

juice,  93 

formula  for  arti  cial,  422 
nervous  control  of,  95 
secretion,  93 
Gastrolipase,  93,  95 
Gelatin,  34 

source  of,  401 
Girdle,  pectoral,  256 

pelvic,  257 
Gland,  alveolus  of,  81 

cells,  16 

ductless,  168 

gastric,  92 

liver,  100 

pancreatic,  102 

racemose  type  of,  81 

salivary,  81 

tissue,  13 
Glomerulus,  221 
Glottis,  84,  404 
Glucose,  43 
Gluten,  29 

Glycerin  from  fats,  104 
Glycogen,  31,  119 
Goitre,  170 
Grafting,  skin,  231 
Growth,  of  cells,  19 

in  general,  36 
Gullet,  84,  404 
Gymnastics,  285 

Habits,  reflex  action  and,  318 
Haemoglobin,  124 

in  respiration,  202 
Hair,  231 
Health,  municipal,  391 

officers,  392 

problems,  public  control  of,  395 
Hearing,  sense  of,  369 
Heart,  cause  of  beat,  144 

defects  in,  143 

demonstration  of  action  of,  407 

events  of  beat,  137 

location  and  structure  of,  136 

muscle,  281 

rate  of  beat,  141,  143 

regulation  of  beat,  145 

sounds,  141 

ventricles  of ,  137 

work  done  by,  143 


432 


INDEX 


Heat,  amount  used  in  a  day,  48 

artificial,  386 

and  cold,  sense  of,  234 

influence  of,  on  circulation,  162 

loss  of,  240 

nerves  perceiving,  234 

regulation  of,  239,  242 

rigor  of  muscle,  279 
Hemorrhage,  185 
Hepatic  duct,  101 
Hip,  257 

disease,  185,  287 

joint  at,  267 
Hookworm,  111 
Hormones,  169 
Hot  and  cold  spots,  413 
House  construction,  384 
Humerus,  256 
Humor,  aqueous,  344 

vitreous,  344 
Hydrochloric  acid  in  gastric  juice, 

93 
Hygiene,  municipal,  391 

personal,  374 

social,  378 
Hyperopia,  353 

Idiocy,  325 

Images,  formation  of,  in  eye,  345 
Illumination,  intensity  of,  360 
Immunity  against  bacteria,  71 

active,  382 

artificial,  382 
Impulse,  theories  of  nerve,  319 
Incisor  teeth,  75 
Incus,  365 

Indigestion,  alcohol  and,  108 
Infection,  378  i 

Influenza,  135,  143 
Inoculation,  382 
Insanity,  325 
Inspiration,  192 
Insurance  companies,  and  users  of 

alcohol,  335 
Intercostal  muscles,  191 

nerves,  195 
Intestinal  tract,  diseases  of,  109 
Intestine,  large,  105 

small,  99 
Involuntary  muscle,  280 
Iodine,  for  ^tarch  tests,  422 
Iris,  344 


Iron  in  blood,  202 
Isolation  periods,  380 

Jaundice,  226 

urine  in,  227 
Joints,  264 

ball  and  socket,  267 

hinge,  265 

imperfect,  264 

injuries  to,  268 

pivot,  268 

Katabolism,  35 
Kidney,  cortex  of,  220 

of  a  sheep,  413 

pelvis  of,  219 
Kidneys,  excretion  of,  in  relation 
to  proteid,  32 

structure  of,  219 
Knee  joint,  265 

Lachrymal  canals,  175,  341 

glands,  341 
Lactase,  104 
Lacteals,  113,  119 

demonstration  of,  406 
Lacunae  of  bone,  263 
Lamellae  of  bone,  263 
Larynx,  177,  210 

cartilage  of,  211 

of  a  sheep,  412 
Lashes  of  eyes,  341 
Laxatives,  374 
Leg,  blood  vessels  to,  158 

bones  of,  257 

nerves  to,  305 
Legumen,  29 
Lens,  the,  344 

change  of  form  in,  of  eye,  351 
Lens,  p&,ssage  of  light  through,  347 
Leucocytes,  126 
Lids  of  eyes,  340 
Life,  indoor,  206 

length  of,  and  alcohol,  ,336 

outdoor,  182 
Ligaments,  266,  274 

capsular,  266 

crucial,  266 

suspensory,  345,  351 
Light,  effect  of  flickering,  360 

effect  of,  in  cy^,  356 

focus  of,  347 

kinds  of  artificial,,  385 


INDEX 


433 


Lime  water,  formula,  423 

Lipase,  103 

Liver,  function  of,  101 

secretion  of,  101 

storage  of  sugar  in,  119 

structure  of,  101 

urea  formation  in,  218 
Living  and  non-li\ing  matter,  19,  27 
Location  of  houses,  383 
Lockjaw,  287 

(see  tetanus) 
Lung,  alveolus  of,  179 
Lungs,  air  in,  197 

capacity  of,  197 

coverings  of,  180 

demonstration  of,  412 

structure  of,  179 
Lupus,  184 
Lymph,  ducts,  120 

flow  of,  166 

glands,  169 

system,  165 

vessels,  167,  403 
Lysine,  104 

Malaria,  132 

and  mosquitoes,  133 
Malleus,  364 
Malpighian,  capsule,  220 

pyramids,  219 
Maltose,  104 
Mandible,  255 
Marrow,  259 
Mastication,  75 
Mastoid  cavities,  363 

disease  of,  364,  373 
Matter,  living  and  non-living,  19, 

27 
Meals,  frequency  of,  50 

water  during,  57 
Measles,  71,  385 
Meat,  composition  of,  46 
Meatus  of  ear,  362 
Medicines,  338 
Medulla,  of  brain,  292 

of  hair,  231 

respiratory  center  in,  194 

seat  of  involuntary  activities,  300 

structure  of,  299 

vaso-constrictor  centre  in,  161 


Medullary  sheath  of  nerves,  307 
Meibomian  glands,  341 
Meningitis,  185,  327 
Mesentery,  90 
Metabolism,  35 

summary  of,  224 
Metacarpal  bones,  257 
Metatarsal  bones,  258 
Microbes,  65 
Milk,  action  of  rennin  on,  94 

calcium  in,  260 

composition  of,  46 

proteid  in,  39 

source  of  typhoid.  Ill 
Mind,  need  of  clear,  328 
Molar  teeth,  75 
Mosquitoes  and  malaria,  133 

and  yellow  fever,  134 
Mouth,  74 

breathing  through,  174 

digestion  in,  80 

diseases  of,  85,  176 
Mucous  cells,  173,  176 
Mucus,  74,  180 
Multicellular  organism,  23 
Mumps,  87 
Muscle,  cardiac,  281 

cells,  15 

ciliary,  351 

distribution  of,  273 

effect  of  use  and  disuse  of,  282 

external,  of  eye,  340 

fibres,  275 

internal,  of  eye,  341 

kinds  of,  274 

papillary,  139 

relation  to  nerve,  416 

stapedius,  365,  372 

striped,  274-279 

unstriped,  280 
Muscles  in  body,  main,  279 
Muscular  system,  275 
Mutton,  39 
Myopia,  352 
Myosin,  29 

Nails,  finger,  233 
Narcotics,  330 
Nearsightedness,  352 
Nephritis,  185 


434 


INDEX 


Nerve,  accelerator,  to  heart,  145 

auditory,  367,  371 

cells,  16 

control  over  muscle,  416 

cranial,  304 

endings,  309 

fibres,  307 

impulse,  319 

inhibitor,  to  heart,  145 

olfactorv,  175,  291 

:)ptic,  291,  356 

iecretory,  82,  95,  237 

spinal,  305 

tissue,  13 
Nerves,  afferent,  306,  310 

axon  of,  307 

cardiac,  145 

efferent,  306,  313 

ganglia,  305,  311 

intercostal,  195 

sympathetic,  145,  324 

to  diaphragm,  195 
Nervous   system,   preservation   of, 
377 

prostration,  326 

system,  289,  310,  340,  362 
central,  289 
peripheral,  304 
Neural  foramina,  252 
Neurons,  310 
Nitrogen,  in  body,  26 

in  respiration,  203 

in  proteid,  30 

in  urea,  31,  218 
Nodes  of  nerve  fibres,  307 
Nose,  173 

cilia  in,  174 
Nucleus  of  cells,  18 

Oesophagus,  84,  88 
Olein,  45 
Olfactory,  cells,  176 

nerves,  175 
Opiates,  use  of,  330 
Optic,  chiasma,  291 

nerves,  291,  356 
Organ  of  Corti,  369 
Organism,  definition  of,  11 

multicellular,  23 

unicellular,  22 
Os  innominatum,  258 


Osmosis,  114 

demonstration  of,  406 
Osteoblasts,  260 
Osteoclasts,  260 
Ossification,  264 
Oxidation,  30,  34,  238 
Oxygen,  breathing,  203 

in  body,  27 

method  of  making,  423 

relations  of,  to  blood,  201 
Oysters  source  of  typhoid,  111,  393 

Pain,  sense  of,  96,  235 

Palate,  79 

Palmatin,  45 

Pancreas,  secretion  of,  103,  171 

structure  of,  102 
Pancreatic  juice,  artificial,  422 

secretion,  103 
Papillae  of  dermis,  234 

on  tongue,  78 
Papillary  muscles,  139 
Paralysis,  326 
Parasites  in  food,  52 
Parotid  gland,  81 

Pasteur's  solution,  formula  for,  422 
Patella,  266 
Peas,  40,  47 
Pelvis,  bones  of,  257,  267 

of  kidney,  219 
Pepsin,  93 
Peptone,  94,  103 
Pericardium,  136 
Perilymph,  365 
Periosteum,  258,  261 
Peristalsis,  in  intestine,  100 

in  oesophagus,  89 

in  ureters,  223 
Peritoneum,  90 
Peritonitis,  109 
Perspiration,  235 

and  heat  regulation,  241 

salt  in,  237 
Physiology,  definition  of,  10 
Phalanges,  257 
Pharynx,  83,  85 

ciUa,  in  84 

demonstration  of,  404 
Pia  mater  of  brain,  290 

of  cord,  301 


INDEX 


435 


Pigment,  in  hair,  231 

in  retina,  355 

in  skin,  230 
Pillars  of  fauces,  83 
Pimples,  cause  of,  131 
Pitch,  of  voice,  213 

perception  of,  370 
Pituitary  body,  291 
Plasma,  123 
Playgrounds,  394 
Pleura,  90,  180 

inflammation  of,  189 
Pleurisy,  189 

Plexus,  brachial  and  lumbar,  305 
Pneumonia,  183 
Poisoning,  blood,  131 
Pons  VaroUi,  292 
Portal  blood  system,  118,  150 
Potatoes,  47 
Poultry  as  food,  39 
Pressure,  blood,  154 
Primitive  sheath  of  nerves,  307 
Pronunciation,  214 
Prostration,  nervous,  326 
Proteid,  as  fuel,  30 

as  tissue  builder,  28 

disadvantages  of,  30 

elements  in,  28 

expense  of,  42 

in  bread,  39 

in  milk,  39 

kinds  of,  29 

nitrogen  in,  30 

per  cent  of,  in  foods,  39 

relation  of  kidneys  to,  31 

tests  for,  400 
Protoplasm,  17 

demonstration  of  living,  399 
Protozoa,  cultures  of,  399 
Ptyalin,  82 
Pulmonary,  arteries,  139 

veins,  141 
Pulse,  142,  157 

demonstration  of,  408 
Pupil  of  eye,  344 
Purple,  visual  in  eye,  355 
Pyloric  valve,  91 
Pyramids,  Malpighian,  219 

Quarantine  laws,  390 

Racemose  type  of  gland,  81 


Radius,  256 

Railroad    companies    and  users  of 

alcohol,  335 
Ration  for  a  day,  49 
Rectum,  106 
Reflex  action,  312,  314 

and  gastric  secretion,  95 

and  habits,  318 

and  salivary  secretion,  82 
Reflex  action,  relation  to  conscio' 

centers,  317 
Renal  blood  vessels,  221  ■* 

organs,  219 
Rennin,  93 

action  of,  on  milk,  94 
Repair  of  cells,  20 
Respiration,  cause  of  movements  of, 
199 

center  of,  194 

chemistry  of,  200 

diseases  of  organs  of,  181 

external,  193 

function  of,  172 

internal,  193 

mechanism  of,  190 

nitrogen  in,  203 

rate  of  movements  in,  196 
Retina,  344,  354,  355 

pigment  in,  355 
Rheumatism,  287 
Ribs,  253 
Rice,  47 
Rickets,  53 
Rods  in  retina,  355 
Rugae  in  stomach,  92 

Saccharose,  43 
Saccule,  366 
Sacrum,  253 
Saliva,  63,  81 
Salivary  glands,  81 

demonstration  of,  404 
Salt  in  food,  53 

and  condiments,  375 

in  perspiration,  237 

in  urine,  222 
Salt  solution,  formula,  423 
Sarcolemma,  275 
Scapula,  256 
Scarlet  fever,  71 
School,  hygiene,  383 

nurses,  390 


436 


INDEX 


Sclerotic,  343 
Scrofula,  185 
Secretion,  gastric,  93 

lachrymal,  341 

liver,  101 

pancreatic,  103,  171 

salivary,  81 
Semicircular  canals,  366 
Sense,  of  hearing,  368 

heat  and  cold,  234 

pain,  96,  235 

sight,  354 

smell,  175 

taste,  79 
Serum,  128 
Sewage,  389 
Shock,  nervous,  326 
Shoes,  270 

proper  fitting  of,  415 
Shoulder,  256 
Sight,  354 

Sigmoid  flexure,  106 
Sinuses,  air,  214 
Skeleton,  250 

parts  of,  where  obtainable,  421 
Skin,  care  of,  244 

excretion  through,  235 

grafting,  230-231 

pigment  in,  230 

protection  from  germs,  235 

structure  of,  228 
Sleep,  322 

as  hygienic  measure,  377 
Smallpox,  71,249 
Smell,  175 
Socket  of  eyes,  340 
Soimd,  loudness  of,  371 

perception  of,  369 

quaUty  of,  372 
Spinal  column,  251 
Spinal  cord,  291 

as  conductor,  405 

as  conductor  of  impulses,  302 

ganglion,  305 

method  of  preparing  sheep's,  417 

nerves,  418 
structure  of,  301 
demonstration  of,  417 
Spleen,  100,  169 
Sprains,  268 

Stapedius  muscle,  365,  372 
Stapes,  365 


Starchy  solution  for  testing,  422 

Steapsm,  103 

Stearin,  45 

Sterilization,  73 

Sternum,  253 

Stimulants  and  the  brain,  329 

Stomach,  91 

Striae  of  muscle,  275 

Street  cleaning,  394 

Strychnin,  330 

Sublingual  gland,  81 

Submaxillary  gland,  81 

Suffocation,  209 

Sugar,  31 

and  diabetes,  226 

stored  in  liver^  119 
Summer  complamt,  109 
Sutures  between  bones,  255 
Swallowing,  88 
Sweat,  evaporation  of,  241 

glands,  237 
Sympathetic  ganglia,  324 

nerves,  145,  324 

demonstration  of,  418 
Synovial  fluid,  265 
System,  blood,  122, 136, 154 

digestive,  74,  88,  98 

excretory,  216 

muscular,  273 

nervous,  289,  310,  340,  362 

respiratory,  172, 190 

sympathetic  nervous,  324 
Systole,  141 

Tapeworms,  52 
Tarsal  bones,  258 
Taste  buds,  79 
Tea,  58,  330 
Teeth,  75-77, 254 
Temperature,  body,  237 

regulation  of,  239 
Temporal  bone,  362 
Tendon,  function  of,  274 

Tetanus'  278,  281,  282,  287,  288 
Thein,  58 
Thoracic  duct,  120 
Thorax,  90 
Throat,  83,  85, 176 
Thrombin,  129 
Thyroid  cartilage,  211 
glands,  170 


INDEX 


437 


Tibia,  258 

Tissue,  bone,  12,262 

builder,  proteid  as,  28 

connective,  13 

definition  of,  12 

kinds  of,  12 
Tissues,  permanent  preparation  of, 

399 
Tobacco,  337 
Tongue,  78 
Tonsilitis,  85 
Tonsils,  83 
Toothache,  77 
Touch,  234 
Toxin,  381 
Trachea,  177 

demonstration  of,  410 
Tract,  alimentary,  74 

ascending  nerve  in  cord,  303 

descending  nerve  in  cord,  303 
Trichina,  52 
Trypsin,  103 
Tryptophane,  104 
Tuberculosis,  71, 184-189 
Tubules,  urinary,  220,  222 
Turbinated  bones  in  nose,  173 
Tympanic,  cavity,  363 

membrane,  362 

tensor  muscle  of,  365,  372 
Tympanum,  363 
Typhoid  fever,  71, 110 

milk,  oysters,  water,  sources  of, 
111 

Ulna,  256 

Unioellular  organism,  22 

Urea,  excretion  of,  221 

formula  of,  218 

making  of,  218 

nitrogen  in,  31,218 
Ureters,  219,  223 
Urethra,  224 
Urine,  222 

in  jaundice,  226 

salt  in,  222 
Utricle,  366 
Uvula.  80 


Vagus    nerves,    relation    to    heart, 
145 

relation  to  lungs,  196 
Value  of  food,  38 
Valves,  cardiac,  139,  141 

in  lymph  ducts,  120 

in  veins,   151 
Vaso-motor  system,  159 
Veal,  39 

Vegetables,  43,  47 
Vegetarianism,  51 
Veins,  145 

main,  in  body,  148 

portal,  118,  150 

pulmonary,  141 

structure  of,  151 
Venae  cavae,  137,  149 
VentQation,  206,  387 
Ventricles  of  brain,  293 

of  heart,  137 
Vertebrae,  251 
Vestibule  of  ear,  365 
Vmi,  113 
Vitamines,  45 
Vitreous  humor,  344 
Vocal  cords,  212 
Voice,  210-214 
Voluntary  muscles,  275-279 
Vomiting,  91 

Walking,  and  good  feet,  269 

as  exercise,  285 
Water,  ice,  and,  384 

during  meals,  57 

excretion  of,  in  kidneys,  222 

excretion  of,  in  perspiration,  237 

excretion  of,  in  respiration,  200 

necessity  for,  57,  224 

source  of  t5T)hoid,  111 

supplies,  383 
Wax  in  ears,  363 
Whooping  cough,  71,  87,  381 
Wounds,  danger  from,  288 

ligaturing  after,  156 

Yeasts,  62,  66 

Yellow  fever  and  mosquitoes,  134 


20. 


HIGH     SCHOOL     TEXTBOOKS 


Lake:    GENERAL  SCIENCE 

A  foundation  for  the  sciences  which  usually  come  later  in 
high  school,  and  the  best  practical  training  for  those  who  may 
withdraw  from  school  at  the  end  of  the  Junior  High  School. 

Conn    and    Budington:     ADVANCED   PHYSIOLOGY  AND 
HYGIENE 

Sets  forth  with  great  clarity  the  successful  modern  methods 
of  promoting  good  health. 

Hallett  and  Anderson:    ELEMENTARY  ALGEBRA 

Introduces  this  study  as  a  natural  extension  of  arithmetic, 
and  emphasizes  the  fundamental  principles  and  processes  of  the 
subject.     With  an  abundance  of  problems. 

Bullock:  THE   ELEMENTS   OF  ECONOMICS 

Presents  the  chief  facts  in  the  structure  of  modern  industry, 
and  discusses  with  noteworthy  fair-mindedness  the  readjust- 
ments of  our  industrial  problems. 

Clippinger:  WRITTEN  AND  SPOKEN  ENGLISH 

Meets  the  demand  for  training  in  correct  speaking  and  writ- 
ing with  reference  to  the  needs  of  later  life.  (In  one  and  two 
volume  editions.) 

SILVER  SERIES   OF  ENGLISH  CLASSICS 

Carefully  and  skillfully  edited  by  men  and  women  who  have 
won  distinction  in  both  the  literary  and  the  educational  worlds. 

Gunnison  and  Harley:    LATIN  FOR  THE  FIRST  YEAR 

Simple  in  treatment,  inductive  in  presentation;  with  abun- 
dant supplementary  reading. 

Gunnison  and  Harley :  CAESAR'S   GALLIC   WAR 

Contains  the  text,  grammar,  and  prose  composition  for  second 
year  Latin. 


SILVER,    BURDETT    AND    COMPANY 

BOSTON  NEW  YORK  CHICAGO  SAN  FRANCISCO 


HIGH     SCHOOL     TEXTBOOKS 


Gunnison  and  Harley:  CICERO'S  ORATIONS 

Contains  the  text,  grammar,  and  prose  composition  for  third 
year  Latin. 

Burton:  VERGIL'S  AENEID 

Unique  in  that  the  introduction,  notes,  references,  and  explana- 
tory matter  are  within  the  grasp  of  high  school  students.  Over 
600  lines  of  sight  translation  from  various  Latin  authors. 

Burton:  A  LATIN   GRAMMAR 

Presents  the  essentials  with  the  greatest  possible  simplicity. 

Cardon:  A  PRACTICAL  FRENCH   COURSE 

A  book  which  makes  for  actual  facility  in  speaking,  reading, 
and  writing  French. 

Cardon:  MON  PETIT  TROTT 

Text  is  used  as  a  basis  for  oral  and  written  composition  with 
drill  in  French  syntax. 

Wilkins    and    Luria:     LECTURAS  FACILES   CON  EJER- 
CICIOS 

A  reader  for  use  as  soon  as  the  pupil  has  mastered  the  ele- 
ments of  the  Spanish  language. 

Luria:   CORRESPONDENCIA    COMERCIAL    CON    EJER- 
CICIOS 

A  book  that  will  give  the  power  to  write  a  genuine  Spanish 
letter. 

Rowland :  ZARAGUETA 

A  play  with  practice  in  Spanish  composition. 

Ford:  A  SPANISH  ANTHOLOGY 

Selections  from  the  best  Spanish  poets,  with  notes. 

Parsons:  HIGH   SCHOOL   SONG  BOOK 

Songs  which  enlarge  the  musical  heritage  of  recreational,  as- 
sembly, and  community  singing. 


SILVER,    BURDETT    AND    COMPANY 

BOSTON  NEW  YORK  CHICAGO  SAN  FRANCISCO 


UNIVERSITY  OF  CALIFORNIA 
MEDICAL  SCHOOL  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

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mand may  be  renewed  if  application  is  made  before  expi- 
ration of  loan  period. 


C75 
1919 


Conii,  H.W»  41326 

Advanced  physiology  and 
hjgiene,   by  Ccnn  and  Bud- 
irigton* — Rev»  |ed> 


4t3>!i; 


LIBRARY 


